Add Ceilometer MongoDB jobs to the Tempest experimental
Add Ceilometer MongoDB jobs to the Tempest experimental

That is needed to check if Tempest Ceilometer notification tests
are running okay in case of MongoDB chosen as a backend - there
was this theory after some researches.

Change-Id: Ibba815bc4e9c742fbe4a90ffd1385bf8f56eb4b4

anbangr/osci-project-config,openstack-infra/project-config,osrg/project-config,openstack-infra/project-config,citrix-openstack/project-config,anbangr/osci-project-config,open-switch/infra_project-config,Tesora/tesora-project-config,open-switch/infra_project-config,citrix-openstack/project-config,coolsvap/project-config,coolsvap/project-config,dongwenjuan/project-config,dongwenjuan/project-config,Tesora/tesora-project-config,noorul/os-project-config,osrg/project-config,noorul/os-project-config