Improve logging output and consistency

* Add logging and error handling to scap.log.Stats
* Debug log stack traces for unhandled exceptions in scap.main.*
* Capitalize logging messages
* Reraise IOError in scap.utils.read_dsh_hosts_file with path included

Change-Id: I88e8b3dc14e2eee8eedc5fe6f21c8bbc2b9e4561