Update test_networks.py to v2 of Quantum API

Fixes bugs in the test suite tempest.tests.network.test_networks that prevents
Jenkins gate-tempest-devstack-vm-quantum-full to execute succesfully. The
problem was that the test suite was using v1 of the Quantum API, which
according to the "Quantum API Guide (V2.0)" has been removed from the code
base. Please see note at bottom of:

docs.openstack.org/api/openstack-network/2.0/content/Overview-d1e71.html

The test suite was patched to use operations supported by v2 of the Quantum
API. This required patches in the following files:

1) tempest.common.rest_client was patched to provide the correct end-point for
v2 of the Quantum API

2) tempest.services.network.json.network_client was patched to support create,
delete, list and show operations for the 3 basic abstractions offered by the
Quantum API: networks, sub-networks and ports

3) tempest.tests.network.base was patched to create a network and a subnetwork
using v2 Quantum API operations.

4) tempest.tests.network.test_networks was patched to invoke v2 Quantum API
operations. Individual tests invoking obsolete operations were eliminated

Fixes bug 1131458
Fixes bug 1159229

Change-Id: I320c46f2a42d8fd9dbfd496e8f357e21eb1c9259
(cherry picked from commit cc939612b3aaff0acbe51e2175cd39b9c080f858)