Fix spurious error msgs from live-boot about failed mounts…

.. and directories already existing

> mount: mounting /dev/sr0 on /run/live/persistence/sr0 failed: No such device
> mount: mounting /dev/vda on /run/live/persistence/vda failed: No such device
> mkdir: can't create directory '/run/live/persistence/vda3/rw': File exists
> mkdir: can't create directory '/run/live/persistence/vda3/work': File exists

components/9990-misc-helpers.sh

@@ -780,7 +780,7 @@ mount_persistence_media ()
 		then
 			mount_opts="ro,noatime"
 		fi
-		if mount -t "${fstype}" -o "${mount_opts}" "${device}" "${backing}" >/dev/null
+		if mount -t "${fstype}" -o "${mount_opts}" "${device}" "${backing}" >/dev/null 2>&1
 		then
 			echo ${backing}
 			return 0
@@ -1383,8 +1383,8 @@ do_union ()
 			# + a workdir to become mounted
 			# + workdir and upperdir to reside under the same mount
 			# + workdir and upperdir to be in separate directories
-			mkdir "${unionrw}/rw"
-			mkdir "${unionrw}/work"
+			mkdir -p "${unionrw}/rw"
+			mkdir -p "${unionrw}/work"
 			unionmountopts="-o noatime,lowerdir=${unionro},upperdir=${unionrw}/rw,workdir=${unionrw}/work"
 			;;
 	esac