ICS-20: Acknowledgement::Error is incompatible with ibc-go

[plafer]

Bug Summary

Our Acknowledgement::Error once serialized is different from ibc-go.

Details

Compare ibc-go output with our AsRef<u8> Error variant.

Version

v0.27.0

[plafer]

Note that the error output needs to be of the form {"error":"<whatever>"} to be compatible with all versions of ibc-go.

ibc-go did in fact change its error output:

• v3.0.0: {"error":"cannot unmarshal ICS-20 transfer packet data"}

• v5.0.0: {"error":"ABCI code: %d: cannot unmarshal ICS-20 transfer packet data"}

[plafer]

I will close as duplicate of #369, and fix both the success and error scenarios with that issue.