title: Plugins management fails with 404 on SonarQube6.3.1
body: <p>I have migrated from sonarQube 6.2 to sonarQube 6.3.1 today.
  Since then, impossible to manage the pluginsd via the web interface : 
  "POST /sonarqube/api/plugins/update HTTP/1.1" 401 - "xxx:9000/sonarqube/updatecenter/updates"</p>
  
  <p>"POST /sonarqube/api/plugins/uninstall HTTP/1.1" 401 - "xxx:9000/sonarqube/updatecenter/installed"</p>
  
  <p>Any idea?</p>
  
  <p>Please find below multiple logs : 
  <strong>es.log</strong> (no specific error except the warning) : 
  2017.05.09 18:37:03 INFO  es[][o.s.p.ProcessEntryPoint] Starting es
  2017.05.09 18:37:03 INFO  es[][o.s.s.EsSettings] Elasticsearch listening on /127.0.0.1:9001
  2017.05.09 18:37:04 INFO  es[][o.elasticsearch.node] [sonarqube] version[2.4.4], pid[308], build[fcbb46d/2017-01-03T11:33:16Z]
  2017.05.09 18:37:04 INFO  es[][o.elasticsearch.node] [sonarqube] initializing ...
  2017.05.09 18:37:04 INFO  es[][o.e.plugins] [sonarqube] modules [], plugins [], sites []
  2017.05.09 18:37:04 INFO  es[][o.elasticsearch.env] [sonarqube] using [1] data paths, mounts [[/ (/dev/mapper/vbtu13--vg-root)]], net usable_space [22.1gb], net total_space [105.9gb], spins? [possibly], types [ext4]
  2017.05.09 18:37:04 INFO  es[][o.elasticsearch.env] [sonarqube] heap size [990.7mb], compressed ordinary object pointers [true]
  2017.05.09 18:37:04 WARN  es[][o.elasticsearch.env] [sonarqube] max file descriptors [4096] for elasticsearch process likely too low, consider increasing to at least [65536]
  2017.05.09 18:37:09 INFO  es[][o.elasticsearch.node] [sonarqube] initialized
  2017.05.09 18:37:09 INFO  es[][o.elasticsearch.node] [sonarqube] starting ...
  2017.05.09 18:37:09 INFO  es[][o.e.transport] [sonarqube] publish_address {127.0.0.1:9001}, bound_addresses {127.0.0.1:9001}
  2017.05.09 18:37:09 INFO  es[][o.e.discovery] [sonarqube] sonarqube/1jRp0dGhSPGTebMmzIKSLQ
  2017.05.09 18:37:12 INFO  es[][o.e.cluster.service] [sonarqube] new_master {sonarqube}{1jRp0dGhSPGTebMmzIKSLQ}{127.0.0.1}{127.0.0.1:9001}{rack_id=sonarqube, master=true}, reason: zen-disco-join(elected_as_master, [0] joins received)
  2017.05.09 18:37:12 INFO  es[][o.elasticsearch.node] [sonarqube] started
  2017.05.09 18:37:12 INFO  es[][o.e.gateway] [sonarqube] recovered [7] indices into cluster_state
  2017.05.09 18:37:14 INFO  es[][o.e.c.r.allocation] [sonarqube] Cluster health status changed from [RED] to [GREEN] (reason: [shards started [[components][0], [components][0]] ...]).</p>
  
  <p><strong>sonar.log</strong> : 
  --> Wrapper Started as Daemon
  Launching a JVM...
  Wrapper (Version 3.2.3)(impossible to post with my reputation)//wrapper.tanukisoftware.org
    Copyright 1999-2006 Tanuki Software, Inc.  All Rights Reserved.
  2017.05.09 18:37:02 INFO  app[][o.s.a.AppFileSystem] Cleaning or creating temp directory /opt/sonar/sonarqube-6.3.1/temp
  2017.05.09 18:37:02 INFO  app[][o.s.p.m.JavaProcessLauncher] Launch process[es]: /usr/lib/jvm/java-8-openjdk-amd64/jre/bin/java -Dhttp.proxyHost=10.220.100.56 -Dhttp.proxyPort=8080 -Dhttps.proxyHost=10.220.100.56 -Dhttps.proxyPort=8080 -Djava.awt.headless=true -Xmx1G -Xms256m -Xss256k -Djna.nosys=true -XX:+UseParNewGC -XX:+UseConcMarkSweepGC -XX:CMSInitiatingOccupancyFraction=75 -XX:+UseCMSInitiatingOccupancyOnly -XX:+HeapDumpOnOutOfMemoryError -Djava.io.tmpdir=/opt/sonar/sonarqube-6.3.1/temp -javaagent:/usr/lib/jvm/java-8-openjdk-amd64/jre/lib/management-agent.jar -cp ./lib/common/<em>:./lib/search/</em> org.sonar.search.SearchServer /opt/sonar/sonarqube-6.3.1/temp/sq-process5998520493205071951properties
  2017.05.09 18:37:14 INFO  app[][o.s.p.m.Monitor] Process[es] is up
  2017.05.09 18:37:14 INFO  app[][o.s.p.m.JavaProcessLauncher] Launch process[web]: /usr/lib/jvm/java-8-openjdk-amd64/jre/bin/java -Dhttp.proxyHost=10.220.100.56 -Dhttp.proxyPort=8080 -Dhttps.proxyHost=10.220.100.56 -Dhttps.proxyPort=8080 -Djava.awt.headless=true -Dfile.encoding=UTF-8 -Xmx512m -Xms128m -XX:+HeapDumpOnOutOfMemoryError -Djava.io.tmpdir=/opt/sonar/sonarqube-6.3.1/temp -javaagent:/usr/lib/jvm/java-8-openjdk-amd64/jre/lib/management-agent.jar -cp ./lib/common/<em>:./lib/server/</em>:/opt/sonar/sonarqube-6.3.1/lib/jdbc/mysql/mysql-connector-java-5.1.39.jar org.sonar.server.app.WebServer /opt/sonar/sonarqube-6.3.1/temp/sq-process2409091727178853918properties
  2017.05.09 18:37:35 INFO  app[][o.s.p.m.Monitor] Process[web] is up
  2017.05.09 18:37:35 INFO  app[][o.s.p.m.JavaProcessLauncher] Launch process[ce]: /usr/lib/jvm/java-8-openjdk-amd64/jre/bin/java -Dhttp.proxyHost=10.220.100.56 -Dhttp.proxyPort=8080 -Dhttps.proxyHost=10.220.100.56 -Dhttps.proxyPort=8080 -Djava.awt.headless=true -Dfile.encoding=UTF-8 -Xmx512m -Xms128m -XX:+HeapDumpOnOutOfMemoryError -Djava.io.tmpdir=/opt/sonar/sonarqube-6.3.1/temp -javaagent:/usr/lib/jvm/java-8-openjdk-amd64/jre/lib/management-agent.jar -cp ./lib/common/<em>:./lib/server/</em>:./lib/ce/*:/opt/sonar/sonarqube-6.3.1/lib/jdbc/mysql/mysql-connector-java-5.1.39.jar org.sonar.ce.app.CeServer /opt/sonar/sonarqube-6.3.1/temp/sq-process6009636964843033739properties
  2017.05.09 18:37:47 INFO  app[][o.s.p.m.Monitor] Process[ce] is up
  2017.05.09 18:37:47 INFO  app[][o.s.application.App] SonarQube is up</p>
  
  <p><strong>access.log</strong> : 
  ...............
  10.220.105.4 - - [10/mai/2017:09:29:01 +0200] "GET /sonarqube/api/plugins/installed HTTP/1.1" 200 - "xxx:9000/sonarqube/updatecenter/installed" "Mozilla/5.0 (X11; Linux x86_64; rv:45.0) Gecko/20100101 Firefox/45.0" "AVvuErdqF8rgNMzDAAJT"
  10.220.105.4 - - [10/mai/2017:09:29:01 +0200] "GET /sonarqube/api/plugins/pending HTTP/1.1" 200 45 "<a href="http://vbtu13:9000/sonarqube/updatecenter/installed" rel="nofollow noreferrer">http://vbtu13:9000/sonarqube/updatecenter/installed</a>" "Mozilla/5.0 (X11; Linux x86_64; rv:45.0) Gecko/20100101 Firefox/45.0" "AVvuErdqF8rgNMzDAAJV"
  10.220.105.4 - - [10/mai/2017:09:29:01 +0200] "GET /sonarqube/api/plugins/updates HTTP/1.1" 200 - "xxx:9000/sonarqube/updatecenter/installed" "Mozilla/5.0 (X11; Linux x86_64; rv:45.0) Gecko/20100101 Firefox/45.0" "AVvuErdqF8rgNMzDAAJU"
  10.220.105.4 - - [10/mai/2017:09:29:08 +0200] "GET /sonarqube/api/plugins/pending HTTP/1.1" 200 45 "xxx:9000/sonarqube/updatecenter/available" "Mozilla/5.0 (X11; Linux x86_64; rv:45.0) Gecko/20100101 Firefox/45.0" "AVvuErdqF8rgNMzDAAJX"
  10.220.105.4 - - [10/mai/2017:09:29:08 +0200] "GET /sonarqube/api/plugins/available HTTP/1.1" 200 - "xxx:9000/sonarqube/updatecenter/available" "Mozilla/5.0 (X11; Linux x86_64; rv:45.0) Gecko/20100101 Firefox/45.0" "AVvuErdqF8rgNMzDAAJW"
  10.220.105.4 - - [10/mai/2017:09:29:13 +0200] "POST /sonarqube/api/plugins/install HTTP/1.1" 401 - "xxx:9000/sonarqube/updatecenter/available" "Mozilla/5.0 (X11; Linux x86_64; rv:45.0) Gecko/20100101 Firefox/45.0" "AVvuErdqF8rgNMzDAAJY"</p>