Migrate java/androidmk.go to new system #1

This change migrates some of AndroidMk()s in java/androidmk.go to
AndroidMkEntries(), mainly focusing on deduping test-related helper
funcs.

Test: Soong tests
Test: Built a system image
Test: Manual inspection of diffs
Change-Id: I7810085521600d9ea2df078837688ade41c04825