Disable rgw pollster when aws module not found
Disable rgw pollster when aws module not found

This patch will raise PollsterPermanentError in rgw pollster
to disable those pollsters when requests-aws module not found.

Change-Id: I880ec77467fae026f25e61d04d7dd76e08834b08
Closes-Bug: #1424746

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