[cli-ref] Update python-ceilometerclient to 2.6.1
[cli-ref] Update python-ceilometerclient to 2.6.1

Change-Id: I9c01338fe7727e421dbce851552d4bd4cb31321c

openstack/openstack-manuals,openstack/openstack-manuals,openstack/openstack-manuals,openstack/openstack-manuals