btrfs-progs: add a test case for unknown keys in subvolume trees

The image has the following corrupted key in fs tree:

	item 4 key (257 INODE_ITEM 0) itemoff 15879 itemsize 160
		generation 9 transid 9 size 0 nbytes 0
		block group 0 mode 100644 links 1 uid 0 gid 0 rdev 0
		sequence 1 flags 0x0(none)
	item 5 key (257 UNKNOWN.8 256) itemoff 15879 itemsize 0 <<<
	item 6 key (257 INODE_REF 256) itemoff 15863 itemsize 16
		index 2 namelen 6 name: foobar

This is inspired by a real world memory bitflip, which lead to a bitflip
from 12 to 8, causing the above unknown key type in a subvolume.

Although we will need to properly enhance btrfs-check to handle such
case better, let's start from detecting and report such unknown keys as
an error.

The image is created by inserting an empty item with above unknown key
type.

Signed-off-by: Qu Wenruo <wqu@suse.com>

Author: adam900710

tests/fsck-tests/069-unknown-fs-tree-key/test.sh

@@ -0,0 +1,14 @@
+#!/bin/bash
+#
+# Verify that check can report unknown key types in subvolume trees
+
+source "$TEST_TOP/common" || exit
+
+check_prereq btrfs
+
+check_image() {
+	run_mustfail "unknown keys in subvolume trees not reported as error" \
+		"$TOP/btrfs" check "$1"
+}
+
+check_all_images