Add branch coverage (googleapis#615)

pferate · Jon Wayne Parrott · commit 5190fd70bba7 · 2016-08-11T09:25:09.000-07:00
It was unintentionally dropped during the migration to pytest.
diff --git a/.coveragerc b/.coveragerc
@@ -1,3 +1,6 @@
+[run]
+branch = True
+
 [report]
 omit =
     */samples/*
