In termios.t, avoid reading uninitialised memory in the tests.

In termios.t, avoid reading uninitialised memory in the tests.

If no terminal devices are found, or getattr() fails on all of them, then
the struct termios wrapped by the POSIX:Termios object will consist of
initialised memory. In this case, it's not possible to use getcc() or the
other get*() methods on it.

Try harder to find a terminal device - as well as STDIN, STDOUT and STDERR
also try to open the controlling terminal directly.