Update doc for sample config file issue
Update doc for sample config file issue

Since we have removed the ceilometer.conf.sample file, we should
update the documentation too.

Change-Id: I93ff8bf2f3332d15495d45a5e55e6252da639302
Closes-Bug: #1320761

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