Bug 919563 - Standardize APK generation. r=glandium

This only handles the simple cases: no mobile/android/base (yet).
Bug 903534 - Part 1: Build background-debug.apk. r=glandium

--HG--
rename : mobile/android/moz.build => mobile/android/tests/background/junit3/moz.build
rename : mobile/android/moz.build => mobile/android/tests/background/moz.build
rename : mobile/android/moz.build => mobile/android/tests/moz.build
Bug 903534 - Part 2: Build and release-sign background.apk. r=glandium