add keystone events to definitions
add keystone events to definitions

keystone events are not measurements and do not make much sense as
samples. this patch adds definition for keystone events.

Change-Id: I13b76a71cf434512190615266948293df4d34589
Partial-Bug: #1384874

openstack/ceilometer,sileht/aodh,pczerkas/aodh,redhat-openstack/ceilometer,r-mibu/ceilometer,maestro-hybrid-cloud/ceilometer,cernops/ceilometer,idegtiarov/ceilometer,idegtiarov/ceilometer,pczerkas/aodh,chungg/aodh,ityaptin/ceilometer,fabian4/ceilometer,openstack/aodh,eayunstack/ceilometer,ityaptin/ceilometer,Juniper/ceilometer,chungg/aodh,Juniper/ceilometer,openstack/ceilometer,eayunstack/ceilometer,fabian4/ceilometer,redhat-openstack/ceilometer,openstack/aodh,r-mibu/ceilometer,cernops/ceilometer,isyippee/ceilometer,sileht/aodh,pkilambi/ceilometer,maestro-hybrid-cloud/ceilometer,mathslinux/ceilometer,mathslinux/ceilometer,pkilambi/ceilometer,isyippee/ceilometer