Continue reporting on URL format KeyError

If a report success/failure URL format string refers to a build
parameter or other dict key which does not exist, log the exception
and continue reporting but print the raw format string instead.
Previously Zuul would just fail to report entirely.

Story: #147
Change-Id: Id936921dc6db919e28dea8ca83648b5ebd017b5c
Merge "Continue reporting on URL format KeyError"