Refactor noxfile (GoogleCloudPlatform#686)

Author: Jon Wayne Parrott

.coveragerc

@@ -1,22 +1,11 @@
 [run]
-include =
-    appengine/*
-    bigquery/*
-    bigtable/*
-    blog/*
-    compute/*
-    datastore/*
-    dataproc/*
-    dns/*
-    error_reporting/*
-    language/*
-    logging/*
-    monitoring/*
-    pubsub/*
-    speech/*
-    storage/*
-    translate/*
-    vision/*
+omit =
+    lib/*
+    env/*
+    */.nox/*
+    */conftest.py
+    */google_appengine/*
+
 [report]
 exclude_lines =
     pragma: NO COVER

.travis.yml

@@ -23,8 +23,8 @@ addons:
     - python3.5-dev
 install:
 - pip install --upgrade pip wheel virtualenv
-- pip install nox-automation coverage
+- pip install --upgrade nox-automation coverage
+# Temporarily install this from source.
+- pip install --upgrade git+https://github.com/dhermes/ci-diff-helper.git
 script:
 - ./scripts/travis.sh
-after_script:
-- coverage report