auth: Refactor afsconf_Open failure handler

Refactor the code which returns a failure from afsconf_Open into
a single section, rather than having multiple copies through out
the routine.

Change-Id: I70b3fec98321bf89e6d59055545d5d4193026d28
Reviewed-on: http://gerrit.openafs.org/9293
Tested-by: BuildBot <buildbot@rampaginggeek.com>
Reviewed-by: Derrick Brashear <shadow@your-file-system.com>
Reviewed-by: Jeffrey Altman <jaltman@your-file-system.com>