Updated doc with debug instructions
Updated doc with debug instructions

This commits adds some info about how you can use debugger in
ceilometer.
Currently testr cannot break into debugger, you have to use
alternative test runner to use it.

Change-Id: Ica68da3da5d8162765a79686d29ffd8d8d9cc85f

MisterPup/Ceilometer-Juno-Extension,openstack/ceilometer,pkilambi/ceilometer,pczerkas/aodh,r-mibu/ceilometer,Juniper/ceilometer,sileht/aodh,eayunstack/ceilometer,openstack/aodh,tanglei528/ceilometer,m1093782566/openstack_org_ceilometer,NeCTAR-RC/ceilometer,mathslinux/ceilometer,luogangyi/Ceilometer-oVirt,cernops/ceilometer,chungg/aodh,sileht/aodh,NeCTAR-RC/ceilometer,cernops/ceilometer,pkilambi/ceilometer,froyobin/ceilometer,m1093782566/openstack_org_ceilometer,luogangyi/Ceilometer-oVirt,r-mibu/ceilometer,openstack/aodh,chungg/aodh,MisterPup/Ceilometer-Juno-Extension,eayunstack/ceilometer,tanglei528/ceilometer,Juniper/ceilometer,openstack/ceilometer,isyippee/ceilometer,froyobin/ceilometer,redhat-openstack/ceilometer,idegtiarov/ceilometer,maestro-hybrid-cloud/ceilometer,isyippee/ceilometer,fabian4/ceilometer,NeCTAR-RC/ceilometer,pczerkas/aodh,idegtiarov/ceilometer,tanglei528/ceilometer,mathslinux/ceilometer,redhat-openstack/ceilometer,maestro-hybrid-cloud/ceilometer,fabian4/ceilometer,ityaptin/ceilometer,ityaptin/ceilometer