Added the --pool-only option to subman's list command.

Should we get this message with no matching consumed and pool id only?
```
[subscription-manager (crog/list-pid-only % u=)]$ sudo bin/subscription-manager list --consumed --matches "doesntexist"  --pool-id-only
[subscription-manager (crog/list-pid-only % u=)]$ sudo bin/subscription-manager list --consumed --matches "doesntexist"
No consumed subscription pools matching the specified criteria were found.
```

I think either way would be okay, just not sure if intentional.