Don't use an O(nm) algorithm* and make it more readable by using a dict.

*Most obviously, it does a nested for-loop over the entire other config.
A bit more subtle, it calls .entries(), which constructs a set from the
list for _every_ outer iteration.
Signed-off-by: NDaniel Latypov <dlatypov@google.com>
Reviewed-by: NDavid Gow <davidgow@google.com>
Tested-by: NBrendan Higgins <brendanhiggins@google.com>
Acked-by: NBrendan Higgins <brendanhiggins@google.com>
Signed-off-by: NShuah Khan <skhan@linuxfoundation.org>