vlserver: Allow reading during ubik writes

vlserver: Allow reading during ubik writes

Turn on the new ubik_BeginTransReadAnyWrite functionality for the
vlserver, which allows us to read data from ubik during a conflicting
ubik write lock. When writing, we now update a copy of the
application-level cache, and write back the changes during a commit.

Change-Id: Ica958af704f40e89c2062e43641d883865613802
Reviewed-on: http://gerrit.openafs.org/2106
Reviewed-by: Derrick Brashear <shadow@dementia.org>
Tested-by: Derrick Brashear <shadow@dementia.org>