Robolectric: replace deprecated code & minor optimization

[hermanliang]

RuntimeEnvironment.getRobolectricPackageManager() and RuntimeEnvironment.setRobolectricPackageManager(packageManager) are deprecated in Robolectric 3.2 and will be removed in 3.4
http://robolectric.org/migrating/

[codecov]

Codecov Report

Merging #629 into master will not change coverage.
The diff coverage is n/a.

@@            Coverage Diff            @@
##             master     #629   +/-   ##
=========================================
  Coverage     51.27%   51.27%           
  Complexity     1536     1536           
=========================================
  Files           129      129           
  Lines          9836     9836           
  Branches       1327     1327           
=========================================
  Hits           5043     5043           
  Misses         4385     4385           
  Partials        408      408

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[rogerhu]

Thanks