Test btrfs quota group consistency operations during snapshot delete.  Btrfs
has had long standing issues with drop snapshot failing to properly account
for quota groups. This test crafts a snapshot tree with shared and exclusive
elements. The tree is removed and then quota group consistency is checked.

This issue is fixed by the linux kernel btrfs patch series:
   [PATCH 0/3] btrfs: qgroup fixes for btrfs_drop_snapshot
   [PATCH 1/3] btrfs: add trace for qgroup accounting
   [PATCH 2/3] btrfs: qgroup: account shared subtrees during snapshot delete
   [PATCH 3/3] Btrfs: __btrfs_mod_ref should always use no_quota

Signed-off-by: Mark Fasheh <mfasheh@suse.de>