title: Error 'cannot find reference' occurs when using tensorflow2.0 in PyCharm
body: <p>Following error shows when I import a package, class or method from tensorflow:</p>
  
  <pre><code>Cannot find reference 'keras' in '__init__.py' less... (Ctrl+F1) 
  Inspection info: This inspection detects names that should resolve but don't. Due to dynamic dispatch and duck typing, this is possible in a limited but useful number of cases. Top-level and class-level items are supported better than instance items.
  </code></pre>
  
  <p>This issue did not happen when using preview versions of tensorflow. However, the program still runs normally.
  I find package 'keras' in 'tensorflow.keras' with this error occurs in the coding interface, but it is unable to run when I change to import 'tensorflow.python.keras'. How do I solve this problem?</p>
  
  <p>I am using tensorflow 2.0.0alpha and lastest version of Pycharm</p>
  
  <pre><code>PyCharm 2018.3.5 (Professional Edition)
  Build #PY-183.5912.18, built on February 26, 2019
  Licensed to xxx
  Subscription is active until May 14, 2019
  For educational use only.
  JRE: 1.8.0_152-release-1343-b28 amd64
  JVM: OpenJDK 64-Bit Server VM by JetBrains s.r.o
  Windows 10 10.0
  </code></pre>