Refactor: create a common base for notification tests
Refactor: create a common base for notification tests

this should allow other test classes to mixin the base test and take
advantage of the mocked notifications.

Change-Id: Iac3c54aa4bc015f6018e630395d1403238a6ff59

vivekdhayaal/keystone,maestro-hybrid-cloud/keystone,ajayaa/keystone,mahak/keystone,nuxeh/keystone,klmitch/keystone,rajalokan/keystone,takeshineshiro/keystone,openstack/keystone,rushiagr/keystone,ajayaa/keystone,roopali8/keystone,himanshu-setia/keystone,jonnary/keystone,mahak/keystone,rushiagr/keystone,promptworks/keystone,ilay09/keystone,promptworks/keystone,openstack/keystone,klmitch/keystone,dstanek/keystone,rajalokan/keystone,rajalokan/keystone,himanshu-setia/keystone,promptworks/keystone,dstanek/keystone,rushiagr/keystone,dstanek/keystone,vivekdhayaal/keystone,nuxeh/keystone,idjaw/keystone,roopali8/keystone,mahak/keystone,jumpstarter-io/keystone,jamielennox/keystone,maestro-hybrid-cloud/keystone,jamielennox/keystone,nuxeh/keystone,cernops/keystone,ilay09/keystone,dims/keystone,jumpstarter-io/keystone,takeshineshiro/keystone,idjaw/keystone,openstack/keystone,ilay09/keystone,dims/keystone,cernops/keystone,jumpstarter-io/keystone,jonnary/keystone,vivekdhayaal/keystone