Fix (or suppress) lint warnings and make it fatal again in the build
process.
Additionally, warnings are treated as errors now. If there are
warnings that are not applicable, add @SuppressLint or tools:ignore
to suppress the warning, so code reviewers can be aware of the lint
issue too.
Test: ./gradlew lint
Change-Id: I63c83ff1b95a0817dc2ac777adce0fa9f9ebd45a