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/exercises/basic_tunnel/README.md

@@ -98,7 +98,7 @@ Your job will be to do the following:
 6. **TODO:** Update the deparser to emit the `ethernet`, then `myTunnel`, then `ipv4` headers. Remember that the deparser will only emit a header if it is valid. A header's implicit validity bit is set by the parser upon extraction. So there is no need to check header validity here.
 7. **TODO:** Add static rules for your newly defined table so that the switches will forward correctly for each possible value of `dst_id`. See the diagram below for the topology's port configuration as well as how we will assign IDs to hosts. For this step you will need to add your forwarding rules to the `sX-commands.txt` files.
 
-![topology](./topo.pdf)
+![topology](./topo.png)
 
 ## Step 3: Run your solution