lvm: fix pv_count and pv_names check

Change-Id: I9a3a2e7c7e5ddc4949eb690c1e4613284db9eafc
Signed-off-by: Federico Simoncelli <fsimonce@redhat.com>
Reviewed-on: http://gerrit.ovirt.org/20196
Reviewed-by: Dan Kenigsberg <danken@redhat.com>