Enhance Comm tests (#1564)
Enhance Comm tests (#1564)

This is in preparation to potential changes in the TCP implementation.
I noticed msgpack doesn't currently support bytearrays and I'd rather have
the issue caught cleanly by the test suite:

  https://github.com/msgpack/msgpack-python/issues/224
blaze/distributed,blaze/distributed,mrocklin/distributed,dask/distributed,mrocklin/distributed,mrocklin/distributed,dask/distributed,dask/distributed,dask/distributed