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/vm/Vagrantfile

@@ -5,7 +5,8 @@ Vagrant.configure(2) do |config|
   config.vm.box = "bento/ubuntu-16.04"
   config.vm.provider "virtualbox" do |vb|
     vb.gui = true
-    vb.memory = "2048"
+    vb.memory = 2048
+    vb.cpus = 2
     vb.customize ["modifyvm", :id, "--cableconnected1", "on"]
   end
   config.vm.synced_folder '.', '/vagrant', disabled: true