engine: add qouta mode check in consume storage

Problem: When qouta mode is set to audit, error "no qouta" on storage
was returned

Solution: In checkConsumptionForSpecificStorageQuota we did not make
sure that qouta was set to enforce before returning an error.

Change-Id: I21cc59098ede7044ebde1d544e295300d8b40cb7
Bug-Url: https://bugzilla.redhat.com/906485
Signed-off-by: Noam Slomianko <nslomian@redhat.com>