function getHyperdriveSession (opts) {
  return sessions[createSessionKey(opts)]
}
Gets a hyperdrives interface to the daemon for the given key

@param {Object|string} opts
@param {Buffer} [opts.key]
@param {number} [opts.version]
@param {Buffer} [opts.hash]
@param {boolean} [opts.writable]
@returns {DaemonHyperdrive}