added subcommand networks to list networks

Example output of this subcommand:

```
$ vagrant rackspace networks
==> default: Network Name                         Network CIDR
==> default: private
==> default: public
==> default: vagrant001                           192.168.3.0/24
==> default: vagrant002                           192.168.4.0/24
==> default: vagrant003                           192.168.5.0/24
```
added column Network ID to the network list

```
==> devstack: Network Name                         Network CIDR             Network ID
==> devstack: private                                                       11111111-1111-1111-1111-111111111111
==> devstack: public                                                        00000000-0000-0000-0000-000000000000
==> devstack: vagrant001                           192.168.3.0/24           c7da5d07-ac80-49ca-8575-8822c71bc758
==> devstack: vagrant002                           192.168.4.0/24           f45ba323-dd21-4999-a5d7-c98a3edfb7a3
==> devstack: vagrant003                           192.168.5.0/24           e49a86df-6c98-42d1-a66b-11c80e1252e1
```
Merge branch 'subcommand_list_networks' of github.com:berendt/vagrant-rackspace into berendt-subcommand_list_networks
Merge branch 'berendt-subcommand_list_networks'