gnocchi: configure archive policies on Ceilo side

This creates two archive policies "ceilometer-low" and
"ceilometer-low-rate" in Gnocchi. And use them to create metrics
in Gnocchi.

The archive policies settings can now be configured in
gnocchi_resources.yaml.

This requires upcoming release of coming
(gnocchixyz/gnocchi#655)

Change-Id: Ib804ef4652af9d40338ad970690f6e92f12ed636

Conflicts:
	ceilometer/publisher/data/gnocchi_resources.yaml
	doc/source/admin/telemetry-measurements.rst

(cherry picked from commit bb4692d)
original commit b96b16928ca84bd1c4025c3f996a65e447a8920f
StoryBoard:
“Various backports to core openstack components to pick up fixes”
https://storyboard.openstack.org/#!/story/2003407