Migrate image API tests to resource_* fixtures

Partially-implements bp resource-cleanup

Change-Id: I46bf457bf3ed1cfedc40b77c82fdfbbd4f4ee1e6
Migrate object_storage API tests to resource_* fixtures

Partially-implements bp resource-cleanup

Change-Id: If8398052f2bf50694deeb3ac9edf677a51c6fd6c
Merge "Migrate image API tests to resource_* fixtures"
Merge "Migrate object_storage API tests to resource_* fixtures"
Merge branch 'master' of https://github.com/openstack/tempest