lvmlockd: fix metadata validation when rescanning VG

lvmlockd: fix metadata validation when rescanning VG

When rescanning a VG from disk, the metadata read from
each PV was compared as a sanity check.  The comparison
is done by exporting the vg metadata from each dev to
a config tree, and then comparing the config trees.
The function to create the config tree inserts
extraneous information along with the actual VG metadata.
This extra info includes creation_time.  The config
trees for two devs can easily be created one second
apart in which case the different creation_times would
cause the metadata comparison to fail.  The fix is to
exclude the extraneous info from the metadata comparison.