Improve catch scope and logging for client stop()

This does two things:
1. Catches the more general `TimeoutException`, since those can be thrown.
2. Logs at info level when a timeout is detected.
Log executor on finish
Slight wording change
Merge pull request #741 from pwendell/usability

Fix two small usability issues
Merge branch 'master' of https://github.com/mesos/spark into bootstrap-update

cially if it merges an updated upstream into a topic branch.
Added started tasks to progress bar