document utc naive timestamp
document utc naive timestamp

Fixes bug #1048647

Change-Id: I611e28054d8e0d08b1b4a5343c7f586db7b6fdbb

JioCloud/ceilometer,sileht/aodh,eayunstack/ceilometer,NeCTAR-RC/ceilometer,luogangyi/Ceilometer-oVirt,tanglei528/ceilometer,isyippee/ceilometer,idegtiarov/ceilometer,MisterPup/Ceilometer-Juno-Extension,sileht/aodh,rackerlabs/instrumented-ceilometer,tanglei528/ceilometer,openstack/ceilometer,chungg/aodh,mathslinux/ceilometer,pczerkas/aodh,rickerc/ceilometer_audit,mathslinux/ceilometer,openstack/aodh,idegtiarov/ceilometer,dreamhost/ceilometer,m1093782566/openstack_org_ceilometer,citrix-openstack-build/ceilometer,isyippee/ceilometer,JioCloud/ceilometer,MisterPup/Ceilometer-Juno-Extension,pkilambi/ceilometer,Juniper/ceilometer,NeCTAR-RC/ceilometer,ityaptin/ceilometer,fabian4/ceilometer,luogangyi/Ceilometer-oVirt,fabian4/ceilometer,pkilambi/ceilometer,dreamhost/ceilometer,cernops/ceilometer,shootstar/ctest,maestro-hybrid-cloud/ceilometer,froyobin/ceilometer,m1093782566/openstack_org_ceilometer,Juniper/ceilometer,tanglei528/ceilometer,pczerkas/aodh,citrix-openstack-build/ceilometer,rickerc/ceilometer_audit,JioCloud/ceilometer,shootstar/ctest,r-mibu/ceilometer,chungg/aodh,cernops/ceilometer,redhat-openstack/ceilometer,r-mibu/ceilometer,maestro-hybrid-cloud/ceilometer,eayunstack/ceilometer,openstack/ceilometer,redhat-openstack/ceilometer,NeCTAR-RC/ceilometer,rickerc/ceilometer_audit,openstack/aodh,froyobin/ceilometer,rackerlabs/instrumented-ceilometer,rackerlabs/instrumented-ceilometer,ityaptin/ceilometer,citrix-openstack-build/ceilometer