streams: update .readable/.writable to false

These properties were initially used to determine stream status
back in node v0.8 and earlier. Since streams2 however, these
properties were *always* true, which can be misleading for
example if you are trying to immediately determine whether
a Writable stream is still writable or not (to avoid a "write after
end" exception).

PR-URL: https://github.com/nodejs/node/pull/4083


Reviewed-By: Chris Dickinson <christopher.s.dickinson@gmail.com>