ABFS: Fix issues raised by Yetus

I aggregated the HADOOP-15407 branch into a single patch and posted it on HADOOP-15770 just to get an aggregate report of all current issues raised by Yetus. There was a javac deprecation warning, a number of checkstyle issues, some whitespace issues, and there are a couple of valid javadoc errors I see locally. Let's fix them before we merge.

I see a number of wildcard imports, all for the contents of large classes of configuration constants, and I think those should stay the way they are. There are a number of existing checkstyle issues in WASB, too that are irrelevant for the merge, and there are some field visibility issues in tests that are required that way for the tests to work as designed.