Enable tests to have host-specific parameters. Remove a bunch of todos where we disabled tests because they would not work everywhere.  Now we selectively enable and set constraints on BVTs.

Review URL: http://codereview.chromium.org/1780007
diff --git a/.gitignore b/.gitignore
index ea8ea0d..51dad37 100644
--- a/.gitignore
+++ b/.gitignore
@@ -15,3 +15,6 @@
 # Anything created as a result of running a test
 results.*/
 tmp/
+
+# This file is meant only for local testing
+private_host_attributes_config.py