Add --pvmetadatacopies as a synonym for --metadatacopies in various commands.

Add --pvmetadatacopies as a synonym for --metadatacopies in various commands.

Going forward, we would like to allow users to specify the total
number of metadatacopies in a VG rather than on a per-PV basis.  In
order to facilitate that, introduce --pvmetadatacopes to replace
--metadatacopies everywhere.  We still allow --metadatacopies for
pv commands, but require --pvmetadatacopies for vg commands.
Eventually we will introduce --vgmetadatacopies.  Once we do that,
we should either deprecate --metadatacopies or make it a synonym based
on the command (pvmetadatacopies for pv commands, and vgmetadatacopies
for vg commands).  The latter option would likely just require a simple
'strncpy' check against cmd->command->name to qualify the merge_synonym
call.

Update nightly tests to cover the pvmetadatacopies synonym.

Note that this patch is the result of an eariler review comment for
the implicit pvcreate patches.  Should apply cleanly on top of the
implicit pvcreate patches (I applied after patch 10/10 in that series).

NOTE: This patch will require --pvmetadatacopies for vgconvert as
--metadatacopies is no longer accepted.