Btrfs-progs: add two new test images

This adds two new test images

1) 008-bad-offset-snapshots.  This has a corrupt item with multiple snapshots
pointing to it, to make sure the bad block repair stuff doesn't loop and
actually repairs stuff.  It also requires the dir index repair stuff to pass our
built in tests which is why it's not tied to the same commit.

2) 009-bad-dir-index-name.img. This has a corrupt name in a dir index to make
sure our dir index repair stuff is working properly.

Thanks,

Signed-off-by: Josef Bacik <jbacik@fb.com>
btrfs-progs: Add testcase for leaf-corrupted btrfsck repairing.

Add testcase for leaf-corrupted btrfsck repairing using the new
generate_image.sh method.

Signed-off-by: Qu Wenruo <quwenruo@cn.fujitsu.com>