Rename android.os.Build so it can be dynamically generated

This will allow the android.os.Build class to be generated dynamically
from the Studio side.
In order to allow the "refactoring" of classses like android.os.Build,
Create needed to be modified.

While adding the test, I've also done a small clean-up of the
AsmGeneratorTest to re-use some code.

Bug: http://b.android.com/210345
Test: Added new test to AsmGeneratorTest
Change-Id: Ie4e1209c1c60b7a33cb427dbd556a9741ec8f8b3