Complete IBC Mock testing

[ethanfrey]

This builds on what is done in #253 and adds some simpler demos as defined in our milestone:

Add a mockHandler that plays ping-pong:

• version is "ping" or "pong" (both acceptable)
• on version negotiation the "Try" side will switch the version (if "ping" requested, counterparty does "pong" and visa versa)
• stores a counter in state (starts at 0)
• Packets are JSON, only valid ones look like {"ping": 5}
• Receiver will add the value to the local state and return acknowledgement
• Acknowledgement is either {"error": "message here"} or {"success": {"pong": 14}} or whatever the updated state is
• On receiving acknowledgement, if a success, then that "remoteState" is stored. If error, increment "numErrors"

This handler has "localState" and "remoteState". Receiving a "ping" packet will increment "localState". Getting a "pong" acknowlegdement will set "remoteState".

Once this is build, a few scenarios:

• Proper connection (show version is swapped from original request), sending packets with coordinators, it works well
• Send {"random": "data"} packet and verify we get an "error" acknowledgement back (numErrors == 1)
• Try connecting with invalid version (transfer) and show channel will not get established

[alpe]

on version negotiation the "Try" side will switch the version (if "ping" requested, counterparty does "pong" and visa versa)

I may not got it correct but what I can see in the code is that the Try side can only accept what is sent to it. So either success or error is returned. The relayer sends the version. There are no negotiation rules defined in IBC where the "Try" side can propose something new. It can be custom logic in the relayer though

[ethanfrey]

From our IBC Spec:

The counterparty has a chance for version negotiation in OnChanOpenTry, where the contract can apply custom logic. It provides the protocol versions that the initiating party expects, and the contract can reject the connection or accept it and return the protocol version it will communicate with. Implementing this (contract selects a version, not just the relayer) requires that we support ADR 025. TODO: check with Agoric and cwgoes to upstream any Cosmos SDK changes so this can work out of the box.

Necessary changes are documented in ADR025

This section in particular we should be able to change in the x/wasm/module.go file. If it does not have the desired request, we can make an issue on cosmos-sdk to support the ADR. (I assume it was approved as it was merged to master)