ktest: Make the signal to terminate the console configurable

 Currently ktest sends SIGINT to terminate the console.
 However, there are consoles which do not exit by this signal, for example,
 in my case, "virsh console <guest OS>". In such case, ktest is blocked in
 close_console(). It prevents this automate test.

This patch adds new option CLOSE_CONSOLE_SIGNAL which mean the
signal to terminate the console. Since its default value is "INT",
the original behavior isn't changed.

Link: http://lkml.kernel.org/r/87zjol8pl5.wl%satoru.takeuchi@gmail.com
Signed-off-by: Satoru Takeuchi <satoru.takeuchi@gmail.com>
Signed-off-by: Steven Rostedt <rostedt@goodmis.org>