Modified & add models and requests to support CloudStack network API

Modified & add models and requests to some missing api which is used by Cloud Foundry in bosh-cloudstack-cpi project.

Influenced files and added tests:
```
 create mode 100644 lib/fog/cloudstack/models/compute/firewall.rb
 create mode 100644 lib/fog/cloudstack/models/compute/firewalls.rb
 create mode 100644 lib/fog/cloudstack/models/compute/ipaddress.rb
 create mode 100644 lib/fog/cloudstack/models/compute/ipaddresses.rb
 create mode 100644 lib/fog/cloudstack/models/compute/key_pair.rb
 create mode 100644 lib/fog/cloudstack/models/compute/key_pairs.rb
 create mode 100644 lib/fog/cloudstack/models/compute/nat.rb
 create mode 100644 lib/fog/cloudstack/models/compute/nats.rb
 create mode 100644 lib/fog/cloudstack/models/compute/network.rb
 create mode 100644 lib/fog/cloudstack/models/compute/networks.rb
 create mode 100644 lib/fog/cloudstack/models/compute/ostype.rb
 create mode 100644 lib/fog/cloudstack/models/compute/ostypes.rb
 create mode 100644 lib/fog/cloudstack/models/compute/vlan.rb
 create mode 100644 lib/fog/cloudstack/models/compute/vlans.rb
 create mode 100644 tests/cloudstack/requests/assosiate_ip_address_tests.rb
 create mode 100644 tests/cloudstack/requests/create_vlan_range_tests.rb
 create mode 100644 tests/cloudstack/requests/delete_vlan_range_tests.rb
 create mode 100644 tests/cloudstack/requests/disable_static_nat_tests.rb
 create mode 100644 tests/cloudstack/requests/disassosiate_ip_address_tests.rb
 create mode 100644 tests/cloudstack/requests/enable_static_nat_tests.rb
 create mode 100644 tests/cloudstack/requests/list_vlan_range_tests.rb
```