VM Updates (#83)

- Minor fixes to p4runtime exercise and README
- Adding p4runtime/solution
- Adding p4runtime/topology.json
- Updating .gitignore to include solution directory and topology.json
- Fixing root-bootstrap to exit on errors
- Updating VM name in Vagrantfile
- Setting up VM to automatically log 'p4' user in on startup

P4D2_2017_Fall/exercises/p4runtime/topology.json

@@ -0,0 +1,16 @@
+{
+    "hosts": [
+        "h1",
+        "h2",
+        "h3"
+    ],
+    "switches": {
+        "s1": {},
+        "s2": {},
+        "s3": {}
+    },
+    "links": [
+        ["h1", "s1"], ["s1", "s2"], ["s1", "s3"],
+        ["s3", "s2"], ["s2", "h2"], ["s3", "h3"]
+    ]
+}