Reset number of uploaded bytes for reused context
fix typo in volume delete logic
Check if volume size fits in cluster capacity (bb#668)

Fix tests to honour checking if volume fits in cluster capacity, used
volume size was exceeding cluster capacity. Add test for too high volume
size.
Introduce volume size enforcement (bb#669)
Add test for volume size enforcement.
REVERT ME: Temporarily report current volume usage instead of its size for volume listing
Update volume size on file delete