btrfs-progs: tests: a check test case with orphan dev extent

The fs has the following chunk tree (minor members removed):

	item 0 key (DEV_ITEMS DEV_ITEM 1) itemoff 16185 itemsize 98
		devid 1 total_bytes 536870912 bytes_used 159383552
		io_align 4096 io_width 4096 sector_size 4096 type 0
	item 1 key (FIRST_CHUNK_TREE CHUNK_ITEM 13631488) itemoff 16105 itemsize 80
		length 8388608 owner 2 stripe_len 65536 type DATA|single
		io_align 65536 io_width 65536 sector_size 4096
		num_stripes 1 sub_stripes 1
	item 2 key (FIRST_CHUNK_TREE CHUNK_ITEM 22020096) itemoff 15993 itemsize 112
		length 8388608 owner 2 stripe_len 65536 type SYSTEM|DUP
		io_align 65536 io_width 65536 sector_size 4096
	item 3 key (FIRST_CHUNK_TREE CHUNK_ITEM 30408704) itemoff 15881 itemsize 112
		length 33554432 owner 2 stripe_len 65536 type METADATA|DUP
		io_align 65536 io_width 65536 sector_size 4096

And the following dev tree:

	item 0 key (DEV_STATS PERSISTENT_ITEM 1) itemoff 16243 itemsize 40
		persistent item objectid DEV_STATS offset 1
		device stats
		write_errs 0 read_errs 0 flush_errs 0 corruption_errs 0 generation 0
	item 1 key (1 DEV_EXTENT 13631488) itemoff 16195 itemsize 48
	item 2 key (1 DEV_EXTENT 22020096) itemoff 16147 itemsize 48
	item 3 key (1 DEV_EXTENT 30408704) itemoff 16099 itemsize 48
	item 4 key (1 DEV_EXTENT 38797312) itemoff 16051 itemsize 48
	item 5 key (1 DEV_EXTENT 72351744) itemoff 16003 itemsize 48
	item 6 key (1 DEV_EXTENT 105906176) itemoff 15955 itemsize 48
		dev extent chunk_tree 3
		chunk_objectid 256 chunk_offset 63963136 length 67108864
		chunk_tree_uuid b2408431-a79a-42b6-aadc-4e853d4caa82

Notice the last dev_extent item, which has no corresponding chunk.

The image is created by calling btrfs_insert_dev_extent(), then
btrfs_update_device() to update dev->bytes_used.

This image can be repaired by both original and lowmem modes.

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

Author: adam900710