Catch and log server exceptions

Fixes bug 1133041

Exceptions from the keystone WSGI server can occur and not be logged.
This means keystone will appear to silently crash, so this change
catches these exceptions and logs them so the user can determine
the cause of the crash.

Change-Id: Iecc4b8062fa4e7dbe021627613412b5dfc635432
Merge "Catch and log server exceptions"