Metrix config conflicts in umbrella apps

[rwdaigle]

In an umbrella app, if metrix is initialized individually for each app, the config gets overwritten (last write wins?). Even in umbrella apps, metrix configs should be isolated to that sub-app.

This will require some investigation into expected behavior with umbrella app config...

/cc @duff

[duff]

In my case, I was using the prefix config.