Update repo link for collectd-ceilometer-plugin

Update repo link for collectd-ceilometer-plugin

Since Ceilometer support was removed from the
collectd-ceilometer-plugin[1], the repo name is misleading.
So the repo name needed to be updated [2]

This change updates references to the collectd-ceilometer-plugin
repo to point to collectd-openstack-plugins repo:
* in deployment operations
* in documentation i.e. links to docs

Dependencies:
[1] https://review.openstack.org/#/c/490823/
[2] https://review.openstack.org/#/c/500768/

This is dependant on the repo rename

Change-Id: I43facbd53bca5df3f7e51d978ae2843c187282d4
Signed-off-by: Emma Foley <emma.l.foley@intel.com>