executor: drop --address=127.0.0.1 from kubectl

The kubectl we use is actually OpenShift and the version we're
using does not include support for the `--address` option.

However, based on testing, by default, 127.0.0.1 is the address
it listens on so we can drop that parameter for now.

Change-Id: Ic0f056078ec40189d16350f7ea6529e8c5f9f685

zuul/executor/server.py

@@ -343,7 +343,6 @@ class KubeFwd(object):
                  '--context=%s' % self.context,
                  '-n', self.namespace,
                  'port-forward',
-                 '--address', '127.0.0.1',
                  'pod/%s' % self.pod, ':19885'],
                 close_fds=True,
                 stdout=subprocess.PIPE,