Add min event check in CTS verifier tests

The test may yield false negative pass even if the tester
does not do anything. Add an extra verifier check to assert
the minimum number of samples.

Bug: 134477295
Test: Run test and do nothing - verify fail. Run test and follow
directions - verify pass.

Change-Id: Id5163211306b95671f8b1eea4314ec879627c4fa
1 file changed