Make CollectionTest and Collection8Test abstract.

These classes are meant to be extended, but the test runner
tries to run them anyway which causes a warning message to
surfaced as a test result. Making them abstract allows
them to be used by subclasses.

bug: 28503384
Change-Id: I45c34dde7f045aa6721352508df463c69c2cd8ef
(cherry picked from commit b30ea05f8b793a5dd781bf45aff6319b0938a299)
2 files changed