Adding starter code and solution for p4runtime exercise (#81)

Summary of changes:
- Adding the p4runtime starter code and solution.
- Adding NO_P4, BMV2_SWITCH_EXE and P4C_ARGS to utils/Makefile
- Updated p4runtime/Makefile to use variables
- Adding conversion functions for match and action param values
- Separating P4Info and P4Runtime libraries
- Updating global README and adding p4runtime/README.md
- Disabling screen saver on VM GUI
- Adding desktop icons for Terminal, Wireshare and Sublime Text
- Updating topo.pdf -> png for Markdown viewing in basic_tunnel and
  p4runtime READMEs

P4D2_2017_Fall/utils/run_exercise.py

@@ -325,11 +325,11 @@ class ExerciseRunner:
                 - A mininet instance is stored as self.net and self.net.start() has
                   been called.
         """
-        self.logger("Starting mininet CLI")
         for s in self.net.switches:
             s.describe()
         for h in self.net.hosts:
             h.describe()
+        self.logger("Starting mininet CLI")
         # Generate a message that will be printed by the Mininet CLI to make
         # interacting with the simple switch a little easier.
         print('')