Introduce lvm short filters.

lvm commands that operate in a known VG can use the known pvs for
filter.

Change-Id: I26f3a7c712b6d7009f5f4e945374b62f18483889
Signed-off-by: Eduardo <ewarszaw@redhat.com>
Reviewed-on: http://gerrit.ovirt.org/17968
Reviewed-by: Ayal Baron <abaron@redhat.com>