common: move _scratch_metadump to common/xfs

_scratch_metadump is really an xfs-specific dump helper, so move it to
common/xfs, add 'xfs' to the name, and convert all users.

Signed-off-by: Darrick J. Wong <djwong@kernel.org>

common/xfs

@@ -453,6 +453,19 @@ _xfs_metadump() {
 	return $res
 }
 
+# Snapshot the metadata on the scratch device
+_scratch_xfs_metadump()
+{
+	local metadump=$1
+	shift
+	local logdev=none
+
+	[ "$USE_EXTERNAL" = yes -a ! -z "$SCRATCH_LOGDEV" ] && \
+		logdev=$SCRATCH_LOGDEV
+
+	_xfs_metadump "$metadump" "$SCRATCH_DEV" "$logdev" nocompress "$@"
+}
+
 # run xfs_check and friends on a FS.
 _check_xfs_filesystem()
 {