Updates for p4runtime example (#71)

* Created p4runtime exercise directory with draft P4 program

* Updating VM

- Adding p4 to vboxsf group for VirtualBox Shared Folders
- Adding gRPC Python package for p4 runtime
- Setting up VM to use 2 CPUs

* Updating .gitignore for PyCharms and Mac OS

* Adding P4RuntimeSwitch type and support in run_exercises

If the grpc switch target is used, we will instantiate a P4RuntimeSwitch.
Ideally, this will get merged with BMv2's P4Switch and can be removed

* Adding p4 runtime and p4info browser libraries

Also, adding a Makefile for this project

P4D2_2017_Fall/exercises/p4runtime/Makefile

@@ -0,0 +1,10 @@
+include ../../utils/Makefile
+
+# Override build method to use simple_switch_grpc target
+run: build
+	sudo python $(RUN_SCRIPT) -t $(TOPO) -b simple_switch_grpc
+
+# Override p4c step to also produce p4info file
+P4INFO_ARGS = --p4runtime-file $(basename $@).p4info --p4runtime-format text
+$(BUILD_DIR)/%.json: %.p4
+	$(P4C) --p4v 16 $(P4INFO_ARGS) -o $@ $<