cleanup tests/test_winsize.py, decrease timeout

Solaris doesn't seem to send SIGWINCH to child process when
TIOCSWINSZ is sent by ioctl.  Still investigating. Otherwise,
decrease the painfully long timeout and make test more clear.
allow isatty() to fail on some systems

On SVR4-like systems, the master_fd of pty-pair
returned by openpty() does not appear as a terimnal.
Add `echo=True' argument for SRV4-based systems

it is not possible to use .setecho() or .waitnoecho() on
these systems. Add a constructor argument that disables
echo after openpty() but before fork() on such systems.
various setecho/waitnoecho -> echo=False changes