Refs: #3442
Refs: #1733

Pithos has two different version accounting
policies:
* free: do not include object history version size 
to the total account usage
* debit: include object history version size to 
the total account usage
This configurable by
PITHOS_BACKEND_FREE_VERSIONING setting.

Pithos delete container function purges 
the history versions of the including objects.
and should send to the quota holder component
the released disk space *only*  
in the case of debit version accounting policy.

Also the purging function used to return 
the negative of the computed released disk space 
but to the quotaholder component was sent 
its negative.
So, erroneously, the released disk space was
added to the total quota usage.

Provide tests for the following distinct cases:
* free version accounting policy (PITHOS_BACKEND_FREE_VERSIONING=True) 
and `auto` container versioning policy
* free version accounting policy
(PITHOS_BACKEND_FREE_VERSIONING=True) 
and `none` container versioning policy
* debit version accounting policy
(PITHOS_BACKEND_FREE_VERSIONING=False) 
and `auto` container versioning policy
* debit version accounting policy(PITHOS_BACKEND_FREE_VERSIONING=False) 
and `none` container versioning policy