Remove rackspace-fog dependency

New version of 'fog' has loosened the `json` library requirements which means now version should work with on Ubuntu 10.04 and we can get rid of `rackspace-fog` requirement.

I've tested it on Ubuntu 10.04 with the versions listed bellow and everything worked correctly.

```bash
root@test-1004:~# cat /etc/lsb-release 
DISTRIB_ID=Ubuntu
DISTRIB_RELEASE=10.04
DISTRIB_CODENAME=lucid
DISTRIB_DESCRIPTION="Ubuntu 10.04 LTS"
root@test-1004:~# gem -v
1.3.5
```