View source for Exercises pyretic debugging

= Exercise: Pyretic Debugging = 
'''HINT:''' You might have to use the "$ dpctl dump-flows tcp:127.0.0.1:6634" or "mininet> dpctl dump-flows" command frequently.  
** In this debugging exercise, we take solutions available in the Internet for the gardenwall problem and try to fix bugs in it.
** The basic solution is taken from the Internet [https://projects.gwdg.de/projects/mayutan-public/repository/raw/courses/SDN/2017_2018_WS/exercises/pyretic_gardenwall_internetsolution1.py], test if it is able to block h1 when "infected". Note that we will only use the "infected == True" for this exercise.
*** Copy the above code into /home/mininet/pyretic/pyretic/examples as pyretic_gardenwall_internetsolution.py
*** start controller (in /home/mininet/pyretic folder): 
     $pyretic.py pyretic.examples.pyretic_gardenwall_internetsolution
*** start mininet: 
     $ sudo mn --controller=remote --topo=single,3 --mac --arp
*** check h1 ping h2
*** Now infect h1 (in /home/mininet/pyretic/pyretic/kinetic folder): 
     $ python json_sender.py -n infected -l True --flow="{srcmac=00:00:00:00:00:01}" -a 127.0.0.1 -p 50001
**** NOTE: it is a "small L(-l) and not numeric 1"
**** Note what happens on the pyretic window

*** check h1 ping h2. We should be able to observe that this traffic is blocked.

== Now, we move on to the debugging part ==
* check h2 ping h3, what happens? 
* Now, modify the given code to allow h2 traffic to pass through to h3, when h1 is "infected". 
* Now, check if the "exempt" case is working fine too (i.e if h1 is "infected" and "exempt", send it to h3 instead of blocking it)
   $ python json_sender.py -n exempt -l True --flow="{srcmac=00:00:00:00:00:01}" -a 127.0.0.1 -p 50001
** (Extra: Not Needed): Try fixing [https://projects.gwdg.de/projects/mayutan-public/repository/raw/courses/SDN/2017_2018_WS/exercises/pyretic_gardenwall_internetsolution.py this] code for the "infected" case.