Doc: Add OldSample to v2.rst

OldSample is still referenced in controllers/v2.py. In order for samples to be
generated in the documentation (thanks to the sample() class method), it must
also be referenced in doc/source/webapi/v2.rst.

Change-Id: Ie5bfe3aa1bc552630dad56eab3b2f921eb2b7690
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"
Merge "Doc: Add OldSample to v2.rst"