Modifications to Spout code to allow for metric registration

Fixes: #445
Yea, we can leave it as we had before, but then modify summingbird code ( https://github.com/twitter/summingbird/blob/develop/summingbird-storm/src/main/scala/com/twitter/summingbird/storm/StormPlatform.scala#L223) to catch the returning new object after register metrics and then call getSpout on that