Update git submodules

Update git submodules

* Update docs/submodules/barometer from branch 'master'
  - Merge "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>