Change automaticaly generated client_id to an uuid

Curently the automaticaly generated client_id for the freezer scheduler is a concatenation of the tenant_id and the hostname.

There is a high chance of colision with that method.

To mitigate that risk we need to change that automaticaly generated client_id to an uuid.

At registration time, we should register a few informations about the host so it is possible to later find out to wich server that uuid correspond.

We could then get something like:

freezer-scheduler client-list
+------------------------------------------------+--------------------------------------------------------------------------------------+ | client_id | registeration informations |
+------------------------------------------------+--------------------------------------------------------------------------------------+
| 940f3b2f-bd74-45ad-bee7-eb0a7318aa84 | {"hostname": "host1", "registeration_date": "2015-11-05 17:06:15.588788"} |
| 65b4f432-7375-42b6-a9b8-7f654a1e676e | {"hostname": "host2", "registeration_date": "2015-10-25 09:10:36.532792"} |
+------------------------------------------------+--------------------------------------------------------------------------------------+

Notes:
- I think we should keep the current possibility to set an arbitrary client_id (with the "-c" option).
- There is already a descritption field tied to the client_id, we could leverage that. If not, should we keep that field ?

- Once generated, store the id in the freezer-scheduler config file (I think this is the right one).

- Choosen informations: AT REGISTRATION
FQDN
Registration datetime
Os
IP
Call to nova-metadata to get OS infos
last registration time

Clients re-register themselfs evrey ! day/hour (NOT EVERY API-POLL)