abci: minor cleanups in the socket client (#3758)
abci: minor cleanups in the socket client (#3758)

Follow up from #3512

Specifically:

    cli.conn.Close() need not be under the mutex (#3512 (comment))
    call the reqRes callback after the resCb so they always happen in the same order (#3512)

Fixes #3513
tendermint/tendermint,tendermint/tendermint,tendermint/tendermint,tendermint/tendermint