[SuwLib] Turn on fatal lint

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