Enable @TestApi access for instrumentation.

Since introduction of ALLOW_TEST_API_ACCESS, it is now possible to
grant access to test apis for the whole UID, instead of just a starting
process.

This resolves the issue, where a forked test process cannot access @TestApi's.

Bug: 147113465
Test: atest CameraEvictionTest#testBasicCamera2ActivityEviction
Change-Id: I8dd3bbacdb263a3e30539f43d8081f6d78e80155