btrfs: Verify falloc on multiple holes won't leak qgroup reserved data space

btrfs: Verify falloc on multiple holes won't leak qgroup reserved data space

Add a test case where falloc is called on multiple holes with qgroup
enabled.

This can cause qgroup reserved data space leak and false EDQUOT
error even we're not reaching the limit.

The fix is titled:
"btrfs: qgroup: Fix the wrong target io_tree when freeing
 reserved data space"

Signed-off-by: Qu Wenruo <wqu@suse.com>
Reviewed-by: Josef Bacik <josef@toxicpanda.com>
Reviewed-by: Filipe Manana <fdmanana@suse.com>
Signed-off-by: Eryu Guan <guaneryu@gmail.com>