udev: ignore LVs containing PVs

udev: ignore LVs containing PVs

If LVM LVs happen to contain PVs, they are passed to the lvm udev
rule for processing, where they should be ignored.  PVs on LVs
most likely belong to VM images, and don't belong to the host
which sees the LV.  It's unsafe for the host to use these PVs.
Without this change, the LV would be processed by pvscan which
would generally ignore it, either because of the devices file,
or because of the default lvm policy to not consider LVs as
potential PVs.  This change makes the udev rule consistent
with that policy and avoids the unnecessary system messages
produced when pvscan ignores the LV.