Build test-runner/tests

Previous change e254526f inadvertently
removed the line to include the tests/Android.mk file.

(cherry picked from commit 006b7a2b)

Bug: 30188076
Test: make checkbuild
Change-Id: I59bd6ec5d317eb6306642974902e4c061e594aa8
Merged-In: Ia0ba14a70d2232d464420265a7a5f9c4dde3661b