Merge changes Ia17b2bcb,Ic71892c3,Id2b23b9e,I435ee7aa,I85112506, ...

* changes:
  Consolidate *MutatorContext and ModuleContext into BaseModuleContext
  Add test for missing defaults modules with AllowMissingDependencies
  Capture missing dependency error rules
  Share buildDir for android/soong/android tests
  Reimplement AddMissingDependencies
  Add GenerateAndroidBuildActions to DefaultsModuleBase