Fix disable_non_metric_meters referencing
Fix disable_non_metric_meters referencing

Need import it otherwise TestMeterProcessing unit test fails.

Change-Id: Ia6da94364bb4c8fd9647b2caf8f1932b1eb2e0de
Closes-Bug: #1488450

ityaptin/ceilometer,cernops/ceilometer,maestro-hybrid-cloud/ceilometer,eayunstack/ceilometer,eayunstack/ceilometer,isyippee/ceilometer,cernops/ceilometer,maestro-hybrid-cloud/ceilometer,ityaptin/ceilometer,fabian4/ceilometer,openstack/ceilometer,idegtiarov/ceilometer,idegtiarov/ceilometer,redhat-openstack/ceilometer,isyippee/ceilometer,redhat-openstack/ceilometer,openstack/ceilometer,fabian4/ceilometer