Ensure that HostTest are not empty

- Check that the hostTest test count is 0 we reject the
module.
- Add couple of error_prone rules for harness quality.

Test: make cts javac-check -j76 TARGET_PRODUCT=aosp_arm64
WITH_DEXPREOPT=false RUN_ERROR_PRONE=true
./cts-tradefed run cts-unit-tests
Bug: 36362112
Bug: 37854485

Change-Id: I8fc00b51afff90e966c3c9ed395b6be17eb2486f
2 files changed