Fix override_android_app dependency issues.

This change fixes an issue where an android_test could not depened on an
override_android_app or an android_app overridden by one by moving all
override processing to post-deps and forwarding incoming dependencies on
override_android_apps to base android_app modules

Fixes: 132447700
Test: app_test.go
Change-Id: I4ac593be661f541f5ea9823ef97373bee4b186f9