ubik: SDISK_Begin no quorum, wrong db, no transaction

ubik: SDISK_Begin no quorum, wrong db, no transaction

When processing an DISK_Begin RPC verify that there is an active quorum
and that the local database is current.  Otherwise, fail the RPC with
a UNOQUORUM error.

The returned error must be UNOQUORUM instead of USYNC becase the returned
error code will be returned by the coordinator's ContactQuorum_iterate()
to the client that triggered the write transaction.  Most ubik clients
will only retry if the error is UNOQUORUM.

FIXES 131997

Change-Id: Icaa30e6aca82e7e7d33e9171a4f023970aba61df
Reviewed-on: http://gerrit.openafs.org/11689
Tested-by: BuildBot <buildbot@rampaginggeek.com>
Reviewed-by: Daria Brashear <shadow@your-file-system.com>
Reviewed-by: Benjamin Kaduk <kaduk@mit.edu>
Reviewed-by: Jeffrey Hutzelman <jhutz@cmu.edu>
Reviewed-by: Jeffrey Altman <jaltman@your-file-system.com>