Add cleanup to Mininet installation script

While installing fresh version of LINC-Switch we clean compiled files
and generated releases.
(Motivated by FlowForwarding/LINC-Switch#247).
Include cleaning up LINC-Switch stuff in Mininet cleanup

Mininet cleanup (invoked by bin/mn -c) will now kill all processes
started by linc node and copied releases for Mininet switches.
(FlowForwarding/LINC-Switch#247).
Merge pull request #6 from FlowForwarding/mininet_cleanup

Mininet cleanup