Fixes to some corner cases + support for some missing 'options and

attributes' for backward compatibility

Ticket: CM-1438
Reviewed By:
Testing Done: Tested ifupdown sanity and new functionality

support for:
- -i <interface file>
- template lookup path and move all template handling to a separate
  module template.py
- new ifupdown2 config file /etc/network/ifupdown2/ifupdown2.conf
- bridge_waitport and bridge_maxwait
- moved addons.conf to /var/lib/ifupdownaddons/

pkg/iface.py

@@ -383,6 +383,7 @@ class iface():
             for cname, cvaluelist in config.items():
                 idx = 0
                 for cv in cvaluelist:
+                    if not cv: continue
                     if with_status:
                         outbuf += indent + '%s %s %s\n' %(cname, cv,
                                     self.get_config_attr_status_str(cname, idx))