zfs_copies: do_vol_test must wait for device

Occasionally zfs_copies_* tests which rely on do_vol_test() will fail
because udev hasn't yet created the minor device.  Wait for it.

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

tests/zfs-tests/tests/functional/cli_root/zfs_copies/zfs_copies.kshlib

@@ -104,6 +104,8 @@ function do_vol_test
 
 	log_must $ZFS create -V $VOLSIZE -o copies=$copy $vol
 	log_must $ZFS set refreservation=none $vol
+	block_device_wait
+
 	if [[ $type == "ufs" ]]; then
 		log_must $ECHO y | $NEWFS $vol_r_path >/dev/null 2>&1
 		log_must $MOUNT -F ufs -o rw $vol_b_path $mntp