Update pool allocation with new values on volume creation

Update pool allocation with new values on volume creation

Since commit e0139e3, we update the pool allocation with
the user-provided allocation values.

For qcow2, the allocation is ignored for volume building,
but we still subtracted it from pool's allocation.
This can result in interesting values if the user-provided
allocation is large enough:

Capacity:       104.71 GiB
Allocation:     109.13 GiB
Available:      16.00 EiB

We already do a VolRefresh on volume creation. Also refresh
the volume after creating and use the new value to update the pool.

https://bugzilla.redhat.com/show_bug.cgi?id=1163091
(cherry picked from commit 56a4e9cb613aff9cd6f828c0a9283fba55ac5951)