Add netifrc renderer for gentoo

This adds a netifrc renderer infrastructure and some unit tests
to test you code try running 

you can run the unit tests with:

nosetests tests/unittests/test_net.py
nosetests tests/unittests/test_net.py:TestNetifrc
nosetests tests/unittests/test_net.py:TestNetifrc.testsimple_render_small

I'd get testsimple_convert_and_render working first.
diff --git a/cloudinit/net/netifrc.py b/cloudinit/net/netifrc.py
new file mode 100644
index 0000000..7deade3
--- /dev/null
+++ b/cloudinit/net/netifrc.py
@@ -0,0 +1,59 @@
+# vi: ts=4 expandtab
+#
+#    This program is free software: you can redistribute it and/or modify
+#    it under the terms of the GNU General Public License version 3, as
+#    published by the Free Software Foundation.
+#
+#    This program is distributed in the hope that it will be useful,
+#    but WITHOUT ANY WARRANTY; without even the implied warranty of
+#    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+#    GNU General Public License for more details.
+#
+#    You should have received a copy of the GNU General Public License
+#    along with this program.  If not, see <http://www.gnu.org/licenses/>.
+"""
+This supports rendering output format for netifrc that is used in gentoo.
+
+https://wiki.gentoo.org/wiki/Netifrc
+"""
+
+import copy
+import glob
+import os
+import re
+
+from . import renderer
+
+from cloudinit import util
+
+
+class Renderer(renderer.Renderer):
+    """Renders network information in a /etc/network/interfaces format."""
+
+    def __init__(self, config=None):
+        if not config:
+            config = {}
+        # config is used as in debian to affect some of the paths
+        # that would be written.
+
+    def render_network_state(self, target, network_state):
+        # this actually renders the NetworkState object state into the
+        # correct format used by the target OS
+        
+        # ...
+
+        # create symlinks
+        for iface in network_state.iter_interfaces():
+            _create_network_symlink(iface['name'], target)
+
+
+def _create_network_symlink(interface_name, target):
+    file_path = os.path.join(
+        target, 'etc/init.d/net.{name}'.format(name=interface_name))
+    if not os.path.islink(file_path):
+        # attempt to do the links as relative
+        log.debug('ln -s ../../etc/init.d/net.lo {file_path}'.
+                  format(file_path=file_path))
+        os.symlink('../..//etc/init.d/net.lo',
+                   '{file_path}'.format(file_path=file_path))
+
diff --git a/tests/unittests/test_net.py b/tests/unittests/test_net.py
index 41b9a6d..65d5f2e 100644
--- a/tests/unittests/test_net.py
+++ b/tests/unittests/test_net.py
@@ -1,6 +1,7 @@
 from cloudinit import net
 from cloudinit.net import cmdline
 from cloudinit.net import eni
+from cloudinit.net import netifrc
 from cloudinit.net import network_state
 from cloudinit.net import sysconfig
 from cloudinit.sources.helpers import openstack
@@ -681,6 +682,51 @@ class TestEniRoundTrip(TestCase):
             files['/etc/network/interfaces'].splitlines())
 
 
+class TestNetifrc(TestCase):
+    def setUp(self):
+        super(TestCase, self).setUp()
+        self.tmp_dir = tempfile.mkdtemp()
+        self.addCleanup(shutil.rmtree, self.tmp_dir)
+
+    def _render_and_read(self, network_config=None):
+        ns = network_state.parse_net_config_data(network_config)
+        renderer = netifrc.Renderer()
+        renderer.render_network_state(self.tmp_dir, ns)
+        return dir2dict(self.tmp_dir)
+
+    def testsimple_convert_and_render(self):
+        network_config = eni.convert_eni_data(EXAMPLE_ENI)
+        files = self._render_and_read(network_config=network_config)
+
+        # files now is a dictionary of files under tmpdir
+        # (dir2dict does not support symlinks... fixes welcome)
+        # so just go through and look at the files that they are what
+        # you think.
+
+        # the Eni test case above has static expected results for
+        # some files, or you can do whatever you want.
+        self.assertEqual(
+            RENDERED_ENI.splitlines(),
+            files['/etc/network/interfaces'].splitlines())
+
+    def testsimple_render_all(self):
+
+        entry = NETWORK_CONFIGS['all']
+        files = self._render_and_read(network_config=yaml.load(entry['yaml']))
+
+        # check this looks as expected
+        print("files look like: %s" % files)
+        self.assertTrue(1 == 0)
+
+    def testsimple_render_small(self):
+        entry = NETWORK_CONFIGS['small']
+
+        # check this looks as expected
+        print("files look like: %s" % files)
+        self.assertTrue(1 == 0)
+
+
+
 def _gzip_data(data):
     with io.BytesIO() as iobuf:
         gzfp = gzip.GzipFile(mode="wb", fileobj=iobuf)