Eliminate unnecessary search for test cases
Eliminate unnecessary search for test cases

As all unit tests lie in `ceilometer/ceilometer/tests`,
the test_command should use `ceilometer/tests` instead of `ceilometer`.

Change-Id: Idb1dade44a06c71fb5e64ca875b71633def110a5
Closes-Bug: 1368509

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