Cloudkitty metric.yml override option

Hi,

I'm deploying Openstack using kolla-ansible and that's beautiful. Please, let me contribute with some point that's I found and I thought we can change to make it better.

I'm deploying Cloudkitty (Rating Module) and I found some issues in Gnocchi, Ceilometer an Cloudkitty that you might change to improve the usability.

1. metrics.yml is fixed inside container and can't be override. That file is useful if you need to add more services than the default or change service names.

2. It was be nice if Ceilometer pipeline.yaml might be override. At that moment kolla-ansible Ceilometer deploy just allow polling.yaml override.

3. You may thought useful include Redis storage option do Gnocchi. I made a handmade configuration and it seems cool. Was something like that.

globals.yml

gnocchi_backend_storage: "redis"

gnocchi.conf

[storage]
driver = redis
redis_url = redis://admin:admin@192.168.1.1:26379?sentinel=kolla&socket_timeout=60&retry_on_timeout=yes