fstests: btrfs: add a new test case to verify quick qgroup inherit

fstests: btrfs: add a new test case to verify quick qgroup inherit

[BUG]
There is a bug report that simple quota exposed a bug in the quick
qgroup inherit, that if there is a multi-level qgroup parent
relationship, only the direct parent got updated.

[TEST CASE]
The test case will create the following subvolume and qgroups first:

- A new subvolume at '/subv1'
- Qgroup 1/1
- Qgroup 2/1

And subvolume '/subv1' is assgiend to qgroup 1/1, so 1/1 is the direct
parent.
Then qgroup 1/1 is also assigned to 2/1, so 2/1 is an indirect parent of
subvolume '/subv1'.

Then the trigger part is to creating a snapshot of '/subv1' and also
assigned the new snapshot into qgroup 1/1 during the snapshot creation.

Since 1/1 is the parent of '/subv1' and the new snapshot, and qgroup 1/1
fully owns '/subv1', we can do a quick inherit.

After the triggering part, just finish the test case and the fsck after
the test case should detect any qgroup inconsistency.

Signed-off-by: Qu Wenruo <wqu@suse.com>
Reviewed-by: David Sterba <dsterba@suse.com>
Signed-off-by: Zorro Lang <zlang@kernel.org>