vgchange: separate change locktype and allow recovery

vgchange: separate change locktype and allow recovery

Add an independent command definition for "vgchange --locktype",
and split the implementation out of the set of common metadata
changes.  It is unlike normal metadata changes, and can only
be run by itself.  (Changing the lock type is similar in
principle to changing the VG name or the VG system ID; it
effects the ability of any host to see or access the VG.)

At some point this command lost the ability to forcibly change
the lock type of a shared VG to "none" (making it a local VG).
This can be necessary to repair shared VGs (e.g. recovery steps
that occur in vg_read are disabled for shared VGs because
they are not locked properly, or recovering sanlock locks
when the PV holding them is lost.)

"vgchange --locktype none --lockopt force VG" is used as the
method of forcing the shared VG to become local so that it
can be repaired.