title: build_native.py fails with error: Build dynamic library for project .. fails
body: <p>I have already installed cocos2d-x 3.0 and try to build an android version but when I run ./build_native.py, it was failed with error</p>
  
  <pre><code>File "./build_native.py", line 89, in do_build
  raise Exception("Build dynamic library for project [ " + app_android_root + " ] fails!")
  Exception: Build dynamic library for project [ /Users/hoangha/Desktop/Enigma/cocos2d-x-3.0/projects/2048-enhanced-version/source/proj.android ] fails!
  </code></pre>
  
  <p>I have read the line 89 in the build_native.py</p>
  
  <pre><code>if os.system(command) != 0:
      raise Exception("Build dynamic library for project [ " + app_android_root + " ] fails!")
  </code></pre>
  
  <p>But I don't understand command os.system(command) in python, so can anybody help me to fix this error.</p>