vlserver: Consolidate VLDB entry server flag definitions

vlserver: Consolidate VLDB entry server flag definitions

Group the definitions of server flags for VLDB entries in one place,
and rename VLSERVER_FLAG_UUID to make its name consistent with the
other flags.
This makes it easier to see the complete set of flags and avoid
conflicts.

Change-Id: I3b326e3d97bc297c0314cfc48f0a066c3ff0415e
Reviewed-on: http://gerrit.openafs.org/6615
Tested-by: BuildBot <buildbot@rampaginggeek.com>
Reviewed-by: Derrick Brashear <shadow@dementix.org>