Fixed flag setting error after data commit to storage
Fixed flag setting error after data commit to storage

The flag "self._has_data" in method _post_commit() of class BaseStorage
can't be set to false after data commit to storage because method _post_commit()
is override in class SQLAlchemyStorage, which caused empty data frame couldn't be
insert to DB and make orchestrator keep retrying when a new tenant is created and
have no data to be collected.

Closes-bug: #1461359

Change-Id: I0d37f6da4c414ae19e67bb6dc1ba8d49a330f628

openstack/cloudkitty,FNST-OpenStack/cloudkitty,stackforge/cloudkitty,stackforge/cloudkitty,FNST-OpenStack/cloudkitty,muraliselva10/cloudkitty,muraliselva10/cloudkitty,openstack/cloudkitty