Ignore ceilometer.conf

ceilometer.conf will be generated after we run tox -egenconfig, it
should be ignored.

Change-Id: Ia6d88892a7c93cfa880e4383bbefa55c069a12d9
Add cmd.polling.CLI_OPTS to option list

polling_namespaces and pollster_list are defined but not present
in etc/ceilometer/ceilometer.conf after run tox -egenconfig.

Change-Id: I27494bfda826a3b2a093a5c0e523acbfa8e4de62