vlserver: Clean up abort logic

vlserver: Clean up abort logic

Clean up the failure logic in the server RPC handlers so that there
is always a single exit point upon aborts. This should make it much
easier to fix the various problems with cleaning up memory when
RPCs fail.

Change-Id: Ia5f8e97c37bf4aca1c8f2597a21eb54d1ba094fb
Reviewed-on: http://gerrit.openafs.org/4772
Tested-by: BuildBot <buildbot@rampaginggeek.com>
Reviewed-by: Derrick Brashear <shadow@dementia.org>