Operation output

This pull request addresses two issues:

1. Fixed bug where the fallback logic for operation's input message type was not correct (it was looking at `operation_name` instead of `port_mesage_type`). For example, see fixed specs where it was (incorrectly) identifying `"sendsms"` as the input name, instead of the correct `"sendsmsRequest"`.

2. Included operation's output to the operations hash, to be consistent with the already-included operations input.

We have tested our changes against the wasabi specs, as well as the specs of savon and savon-multipart, and they all pass (on a local test machine). We will look into the Travis build report ASAP.