Replace 'Ceilometer' by 'Telemetry' in the generated doc

Text strings from ceilometer/api/controllers/v2.py may appear in the
documentation generated for api.openstack.org, where the word 'Ceilometer' has
been removed.

Change-Id: I3a8e333212a33a4775a1cd75da8909b5b14f3230
Merge "Replace 'Ceilometer' by 'Telemetry' in the generated doc"