Adds LOG statements in multiprocess API test

Renames _terminate_workers() to _wait_for_workers_to_end() to accurately
match what is done in that method. Adds a bunch of LOG.info() and
LOG.warn() calls in the various methods in the test to get better
debugging information when bug # 1357578 rears its ugly head.

Change-Id: I6698b7c71ec651c812138c8dd93b1e1b33ee1178
Related-bug: #1357578
Merge "Adds LOG statements in multiprocess API test"