rename resource nitb_iface to ip_address

I would like to use the IP addresses also for OsmoBSC processes, so it is more
than clear now that 'nitb_iface' was the wrong naming choice.

The only distinction we may need in the future is public versus loopback
interface. To add that, we may add a trait to the 'ip_address' resource
like:

  ip_address:
  - addr: 10.42.42.1
    type: public
  - addr: 127.0.0.1
    type: loopback

This way we can substitute public vs loopback addresses flexibly (e.g. using
scenarios).

Change-Id: I3ad583ae7a33f7a7bb56fe78a125f73c56a0e860
diff --git a/selftest/template_test.py b/selftest/template_test.py
index 31d9e80..b7d987c 100755
--- a/selftest/template_test.py
+++ b/selftest/template_test.py
@@ -58,7 +58,7 @@
                         bts_list=(mock_bts0, mock_bts1)
                     ),
                 ),
-            nitb_iface=dict(addr='val_nitb_iface_addr'),
+            ip_address=dict(addr='val_ip_address_addr'),
        )
 
 print(template.render('osmo-nitb.cfg', vals))