title: scanPeriod attribute is required by logback-classic for auto-reload to work
body: <p>Is this a bug in logback classic or am I missing something? <a href="http://logback.qos.ch/manual/configuration.html#autoScan" rel="noreferrer">The documentation</a> is pretty explicit about <code>scanPeriod</code> being an optional attribute:</p>
  
  <blockquote>
    <p>By default, the configuration file will be scanned for changes once
    every minute.</p>
  </blockquote>
  
  <p>However, given a <code>logback.xml</code> file like below:</p>
  
  <pre><code>&lt;?xml version="1.0" encoding="UTF-8"?&gt;
  &lt;configuration debug="true" scan="true" &gt;           
      &lt;appender name="CONSOLE" class="ch.qos.logback.core.ConsoleAppender"&gt;
          &lt;encoder&gt;
              &lt;pattern&gt;%d{yyyy-MM-dd HH:mm:ss.SSS} [%thread] %-5p %c{1}:%L - %m%n&lt;/pattern&gt;
              &lt;charset&gt;utf8&lt;/charset&gt;
          &lt;/encoder&gt;
      &lt;/appender&gt;
      &lt;root level="WARN"&gt;
          &lt;appender-ref ref="CONSOLE" /&gt;
      &lt;/root&gt;
  &lt;/configuration&gt;
  </code></pre>
  
  <p>I get the following output from logback and scan does <strong>not</strong> work.</p>
  
  <pre><code>16:40:56,244 |-INFO in ch.qos.logback.classic.LoggerContext[default] - Could NOT find resource [logback.groovy]
  16:40:56,244 |-INFO in ch.qos.logback.classic.LoggerContext[default] - Could NOT find resource [logback-test.xml]
  16:40:56,244 |-INFO in ch.qos.logback.classic.LoggerContext[default] - Found resource [logback.xml] at [file:/home/jbochenski/acme/acme-func-test/conf/logback.xml]
  16:40:56,323 |-INFO in ch.qos.logback.core.joran.action.AppenderAction - About to instantiate appender of type [ch.qos.logback.core.ConsoleAppender]
  16:40:56,325 |-INFO in ch.qos.logback.core.joran.action.AppenderAction - Naming appender as [CONSOLE]
  16:40:56,331 |-INFO in ch.qos.logback.core.joran.action.NestedComplexPropertyIA - Assuming default type [ch.qos.logback.classic.encoder.PatternLayoutEncoder] for [encoder] property
  16:40:56,354 |-INFO in ch.qos.logback.classic.joran.action.RootLoggerAction - Setting level of ROOT logger to WARN
  16:40:56,355 |-INFO in ch.qos.logback.core.joran.action.AppenderRefAction - Attaching appender named [CONSOLE] to Logger[ROOT]
  16:40:56,355 |-INFO in ch.qos.logback.classic.joran.action.ConfigurationAction - End of configuration.
  16:40:56,356 |-INFO in ch.qos.logback.classic.joran.JoranConfigurator@146ba0ac - Registering current configuration as safe fallback point
  </code></pre>
  
  <p>However if I just change the configuration to add <code>scanPeriod</code> attribute <code>&lt;configuration debug="true" scan="true" scanPeriod="1 minute"&gt;</code> it starts working:</p>
  
  <pre><code>16:43:44,584 |-INFO in ch.qos.logback.classic.LoggerContext[default] - Could NOT find resource [logback.groovy]
  16:43:44,585 |-INFO in ch.qos.logback.classic.LoggerContext[default] - Could NOT find resource [logback-test.xml]
  16:43:44,585 |-INFO in ch.qos.logback.classic.LoggerContext[default] - Found resource [logback.xml] at [file:/home/jbochenski/acme/acme-func-test/conf/logback.xml]
  16:43:44,686 |-INFO in ch.qos.logback.classic.joran.action.ConfigurationAction - Will scan for changes in [file:/home/jbochenski/acme/acme-func-test/conf/logback.xml] 
  16:43:44,686 |-INFO in ch.qos.logback.classic.joran.action.ConfigurationAction - Setting ReconfigureOnChangeTask scanning period to 1 minutes
  16:43:44,688 |-INFO in ch.qos.logback.core.joran.action.AppenderAction - About to instantiate appender of type [ch.qos.logback.core.ConsoleAppender]
  16:43:44,691 |-INFO in ch.qos.logback.core.joran.action.AppenderAction - Naming appender as [CONSOLE]
  16:43:44,700 |-INFO in ch.qos.logback.core.joran.action.NestedComplexPropertyIA - Assuming default type [ch.qos.logback.classic.encoder.PatternLayoutEncoder] for [encoder] property
  16:43:44,727 |-INFO in ch.qos.logback.classic.joran.action.RootLoggerAction - Setting level of ROOT logger to WARN
  16:43:44,727 |-INFO in ch.qos.logback.core.joran.action.AppenderRefAction - Attaching appender named [CONSOLE] to Logger[ROOT]
  16:43:44,727 |-INFO in ch.qos.logback.classic.joran.action.ConfigurationAction - End of configuration.
  16:43:44,728 |-INFO in ch.qos.logback.classic.joran.JoranConfigurator@f6c48ac - Registering current configuration as safe fallback point
  </code></pre>
  
  <p>Using:</p>
  
  <ul>
  <li><code>logback-classic</code>: 1.1.7</li>
  <li><code>slf4j</code>: 1.7.13</li>
  </ul>