Windows: introduce cm_MarkServerDown

Windows: introduce cm_MarkServerDown

Consolidate the operations necessary to mark a server down into a
new routine cm_MarkServerDown()

Reviewed-on: http://gerrit.openafs.org/11445
Tested-by: BuildBot <buildbot@rampaginggeek.com>
Reviewed-by: Jeffrey Altman <jaltman@your-file-system.com>
(cherry picked from commit 15c62a9dd014dc56192c8e880fa6855f5377154e)

Change-Id: Ied2fbb0b7d5c80a928bac6d8c648280b82941a00
Reviewed-on: http://gerrit.openafs.org/11496
Tested-by: BuildBot <buildbot@rampaginggeek.com>
Reviewed-by: Jeffrey Altman <jaltman@your-file-system.com>