Refactor StorageQuotaFull test cases in test_quota
Refactor StorageQuotaFull test cases in test_quota

There were two test cases in test_quota that shared the same name, but
did almost the same thing. After a bit of digging, it looked like most
of the test cases did the almost same thing, so I refactored the common
bits and fixed the test case name duplication.

Partial-Bug: #1259036
Change-Id: I828eea570d358d98520c7201454c03ba174a35ad

dims/glance,scripnichenko/glance,vuntz/glance,JioCloud/glance,kfwang/Glance-OVA-OVF,tanglei528/glance,wkoathp/glance,darren-wang/gl,darren-wang/gl,sigmavirus24/glance,openstack/glance,takeshineshiro/glance,saeki-masaki/glance,stevelle/glance,redhat-openstack/glance,wkoathp/glance,tanglei528/glance,saeki-masaki/glance,jumpstarter-io/glance,takeshineshiro/glance,paramite/glance,akash1808/glance,paramite/glance,scripnichenko/glance,vuntz/glance,akash1808/glance,klmitch/glance,stevelle/glance,sigmavirus24/glance,klmitch/glance,openstack/glance,ozamiatin/glance,redhat-openstack/glance,rajalokan/glance,ozamiatin/glance,kfwang/Glance-OVA-OVF,openstack/glance,JioCloud/glance,jumpstarter-io/glance,dims/glance,rajalokan/glance