Improve config_gen script after introducing new config parameter

New config parameter controllers_listener was introduce and the script
generating LNIC-Switch configuration needs to be modified.
(Motivated by #171).
Add description about running LINC with NOX controller in Mininet

Now LINC-Switch can connect to NOX 1.3 controller through the Mininet.
(Motivated by #171).
Merge pull request #190 from FlowForwarding/issue171

Update docs and config generation script regarding running LINC with NOX on Mininet