Corrected test_fallback_meter_path test case
Corrected test_fallback_meter_path test case

Make sure the test_fallback_meter_path test case won't fail if
/etc/ceilometer/meters.yaml file exists or not.

Closes-Bug: #1486869
Change-Id: I630aa6a2fca48d87fcd7f9584701e461222a9bed

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