Ktest: Add SigInt handling

User can cancel tests and specify handler's behavior using option
'EMAIL_WHEN_CANCELED'.

Link: http://lkml.kernel.org/r/1522094884-22718-3-git-send-email-tianyang.chen@oracle.com

Suggested-by: Dhaval Giani <dhaval.giani@oracle.com>
Signed-off-by: Tim Tianyang Chen <tianyang.chen@oracle.com>
Signed-off-by: Steven Rostedt (VMware) <rostedt@goodmis.org>