btrfs-progs: tests: teach extract_image about packed streams

Packed streams for testing purposes should be packed with 'xz -9' and
use suffix .stream.xz .

Signed-off-by: David Sterba <dsterba@suse.com>

tests/common

@@ -128,6 +128,7 @@ check_image()
 # - dtto compressed by XZ, suffix .raw.xz
 # - meta-dump images with suffix .img
 # - dtto compressed by XZ, suffix .img.xz
+# - compressed send stream, .stream.xz
 extract_image()
 {
 	local image
@@ -154,6 +155,12 @@ extract_image()
 		image=${image%%.xz}
 		mv "$image" "$image".restored
 		;;
+	*.stream.xz)
+		xz --decompress --keep "$image" || \
+			_fail "failed to decompress file $image" >&2
+		image=${image%%.xz}
+		mv "$image" "$image".restored
+		;;
 	esac
 
 	if ! [ -f $image.restored ]; then