Implement notification agent service

In Icehouse, ceilometer-agent-notification is a new service which splits
ceilometer-collector responsibilites.

implement blueprint ceilometer-agent-notification
Change-Id: Iccc660814991e30b12a884a6e6ffd4f581c768c4
Signed-off-by: Emilien Macchi <emilien.macchi@enovance.com>
Move service polling credentials to service_credentials

Change-Id: I74a523bcc1acd18532bb9353b70da63c70e8e325
Closes-bug: #1287939
Merge "Move service polling credentials to service_credentials"
Merge "Implement notification agent service"