Add new network activators to bring up interfaces (#919)

Currently _bring_up_interfaces() is a no-op for any distro using
renderers. We need to be able to support bringing up a single
interfaces, a list of interfaces, and all interfaces. This should be
independent of the renderers, as the network config is often
generated independent of the mechanism used to apply it.

Additionally, I included a refactor to remove
"_supported_write_network_config". We had a confusing call chain of
apply_network_config->_write_network_config->_supported_write_network_config.
The last two have been combined.

1 files changed, 4 insertions, 2 deletions

diff --git a/cloudinit/net/tests/test_network_state.py b/cloudinit/net/tests/test_network_state.py
index fc4724a1..84e8308a 100644
--- a/cloudinit/net/tests/test_network_state.py
+++ b/cloudinit/net/tests/test_network_state.py
@@ -67,11 +67,13 @@ class TestNetworkStateParseConfig(CiTestCase):
 
     def test_missing_version_returns_none(self):
         ncfg = {}
-        self.assertEqual(None, network_state.parse_net_config_data(ncfg))
+        with self.assertRaises(RuntimeError):
+            network_state.parse_net_config_data(ncfg)
 
     def test_unknown_versions_returns_none(self):
         ncfg = {'version': 13.2}
-        self.assertEqual(None, network_state.parse_net_config_data(ncfg))
+        with self.assertRaises(RuntimeError):
+            network_state.parse_net_config_data(ncfg)
 
     def test_version_2_passes_self_as_config(self):
         ncfg = {'version': 2, 'otherconfig': {}, 'somemore': [1, 2, 3]}