Introduce new command 'list-filters' to retrieve
enabled resource filters.

```
command: cinder list-filters --resource=volume

output:
+----------------+-------------------------------+
| Resource       | Filters                       |
+----------------+-------------------------------+
| volume         | name, status, image_metadata  |
+----------------+-------------------------------+

```

Also Added new option '--filters' to these list commands:
1. list
2. snapshot-list
3. backup-list
4. attachment-list
5. message-list
6. group-list
7. group-snapshot-list
8. get-pools

Change-Id: I062e6227342ea0d940a8333e84014969c33b49df
Partial: blueprint generalized-filtering-for-cinder-list-resource
Depends-On: 04bd22c1eb371805a3ce9f6c8915325bc0da2d36
Depends-On: 7fdc4688fea373afb85d929e649d311568d1855a

Following OpenStack Style Guidelines:
http://docs.openstack.org/developer/hacking/#dictionaries-lists
It is not clear as using explicit dictionaries
and help avoid some errors during refactoring.

Change-Id: If29fa568b757e8e08ec2bd8986d08e422db9eee4

Run pylint with
 $ tox -e pylint

(Copied from Cinder with minor changes.)

Change-Id: I9d7f03c44c6da7515b433d6c87f3a1645184d491