Allow piped stdout/stderr use uv_tty_t

There are issues with reading stdin when it is actually attached to a pipe, but
I have run into no problems in writing to stdout/stderr when they are attached
to pipes.
auto merge of #10558 : alexcrichton/rust/faster-stdout, r=pcwalton,pcwalton

There are issues with reading stdin when it is actually attached to a pipe, but
I have run into no problems in writing to stdout/stderr when they are attached
to pipes.