It takes a variable amount of time for the multipath daemon
to create /dev/dm-XX in response to new LUNs being discovered.
The old iscsi_util code only discovered the multipath device
if it was created quickly enough, but in a significant number
of cases, kubelet would grab one of the individual paths and
put a filesystem it on before multipathd could construct a
multipath device.

This change waits for the multipath device to get created for
up to 10 seconds, but only if the PV actually had more than
one portal.