Avoid devices where the lvm metadata is not present (#481698)
The only thing I would change here is:
if dev.strip().lower() == "unknown device"
I know it seems a bit pointless, but since we are relying on the output
of external commands, a point release there could easily change the
output from "unknown device" to something like "UnKnOwN dEvIcE" and
we'll have to figure that out for RHEL 4.19.