Add script creating a copy of the base release

Scrip rel_copy.sh can either create the copy of the base release called
linc or delete such a copy. It takes two arguments: a switch indicating
creation/deletion and the release suffix. The script does not copy
lib/ directory, ERTS and Mnesia files. There are links created to the
lib/directory and the ERTS from the base release. This script also
changes sname parameter for the node. For example the following script
invocation will create a release rel/linc_s1 with sname parameter set to
linc_s1:
./rel_copy.sh -c s1
(Motivated by #240).
Add generating controllers' listener port to config_gen; fix typos

Now config_gen script can also generate controllers' listener
configuration. Some typos were fixed by the way.
(Motivated by #240).
Add controller's scenario for sample Mininet topology

This scenario setup two switches for the topology defined in
MININET_ROOT/custom/topo-2sw-host.py.
(Motivated by FlowForwarding/LINC-Switch#240).
Update LINC/Mininet tutorial after adding support for multiple instances

Now LINC can be run in Mininet topologies with more than one switch.
(Motivated by #240).
Merge pull request #253 from FlowForwarding/multiple-instances

Multiple instances of LINC on Mininet