At normal exit in test_all_modes we don't restore the original termio,
since g_io_channel_shutdown() closes the stdin fd and so the following
tcsetattr on stdin will fail. We also don't restore the termio at signal
exit. Fix both cases by installing an exit hanlder with a dup'ed stdin fd.

Signed-off-by: Imre Deak <imre.deak@intel.com>