common: use mount/umount helpers everywhere

Replace every explicit mount/umount of scratch or test devices with
helper functions. This allows the next patch to add in hooks to these
functions in order to set up & tear down overlayfs on every mount/umount

(also adds _test_unmount(), which didn't exist prior)

[Eryu Guan rebased the patch agains latest master and replaced more
mount/umount with helpers]

Signed-off-by: Eryu Guan <eguan@redhat.com>
Signed-off-by: Eric Sandeen <esandeen@redhat.com>
Reviewed-by: Dave Chinner <dchinner@redhat.com>
Signed-off-by: Dave Chinner <david@fromorbit.com>

check

@@ -439,7 +439,7 @@ for section in $HOST_OPTIONS_SECTIONS; do
 
 	if $RECREATE_TEST_DEV || [ "$OLD_FSTYP" != "$FSTYP" ]; then
 		echo "RECREATING    -- $FSTYP on $TEST_DEV"
-		umount $TEST_DEV 2> /dev/null
+		_test_unmount 2> /dev/null
 		if ! _test_mkfs >$tmp.err 2>&1
 		then
 			echo "our local _test_mkfs routine ..."
@@ -456,7 +456,7 @@ for section in $HOST_OPTIONS_SECTIONS; do
 		fi
 		_prepare_test_list
 	elif [ "$OLD_MOUNT_OPTIONS" != "$MOUNT_OPTIONS" ]; then
-		umount $TEST_DEV 2> /dev/null
+		_test_unmount 2> /dev/null
 		out=`_mount_or_remount_rw "$MOUNT_OPTIONS" $TEST_DEV $TEST_DIR`
 		if [ $? -ne 1 ]; then
 			echo $out
@@ -486,7 +486,7 @@ for section in $HOST_OPTIONS_SECTIONS; do
 	needwrap=true
 
 	if [ ! -z "$SCRATCH_DEV" ]; then
-	  umount $SCRATCH_DEV 2>/dev/null
+	  _scratch_unmount 2> /dev/null
 	  # call the overridden mkfs - make sure the FS is built
 	  # the same as we'll create it later.
 
@@ -679,8 +679,8 @@ for section in $HOST_OPTIONS_SECTIONS; do
 	_wrapup
 	echo
 
-	umount $TEST_DEV 2> /dev/null
-	umount $SCRATCH_DEV 2> /dev/null
+	_test_unmount 2> /dev/null
+	_scratch_unmount 2> /dev/null
 done
 
 interrupt=false