Removes use of timeutils.set_time_override
Removes use of timeutils.set_time_override

The set_time_override function in timeutils was written as a
helper function to mock utcnow for unittests before 'mock' was
generally used. Now that we have mock and fixture, we no longer
need to use it.

Change-Id: I7c3793d7a442dc85aec405041c3c9ce6f7503bd8
Closes-Bug: #1266962

froyobin/ceilometer,r-mibu/ceilometer,pczerkas/aodh,MisterPup/Ceilometer-Juno-Extension,redhat-openstack/ceilometer,cernops/ceilometer,idegtiarov/ceilometer,fabian4/ceilometer,isyippee/ceilometer,idegtiarov/ceilometer,ityaptin/ceilometer,sileht/aodh,pczerkas/aodh,openstack/aodh,NeCTAR-RC/ceilometer,NeCTAR-RC/ceilometer,tanglei528/ceilometer,mathslinux/ceilometer,MisterPup/Ceilometer-Juno-Extension,openstack/aodh,ityaptin/ceilometer,tanglei528/ceilometer,m1093782566/openstack_org_ceilometer,Juniper/ceilometer,froyobin/ceilometer,mathslinux/ceilometer,maestro-hybrid-cloud/ceilometer,eayunstack/ceilometer,sileht/aodh,openstack/ceilometer,isyippee/ceilometer,fabian4/ceilometer,NeCTAR-RC/ceilometer,pkilambi/ceilometer,luogangyi/Ceilometer-oVirt,eayunstack/ceilometer,chungg/aodh,m1093782566/openstack_org_ceilometer,luogangyi/Ceilometer-oVirt,redhat-openstack/ceilometer,Juniper/ceilometer,cernops/ceilometer,pkilambi/ceilometer,openstack/ceilometer,tanglei528/ceilometer,chungg/aodh,maestro-hybrid-cloud/ceilometer,r-mibu/ceilometer