Added TaskSnapshotCacheTest back to presubmit

The problem the test was having was fixed by ag/2179887

Also, fixed NPE during test tear down.

Change-Id: I974fcb9a12928dd4494525f9bae5c7c448657e30
Fixes: 35196891
Bug: 37682538
Test: TaskSnapshotCacheTest
2 files changed