Fix zconfig.sh test 9

Commit ba6a240 adjusted the behavior of 'zfs create -V'. The
caller is no longer guaranteed that udev will have finished
creating the /dev/ entries by the time to command exits. It
is therefore required that we explicitly block waiting for
udev to settle for this test to run reliably.

Signed-off-by: Brian Behlendorf <behlendorf1@llnl.gov>