ktest: Add CONNECT_TIMEOUT to change the connection timeout time

Before ktest issues a reboot, it will try to connect to the target machine
to make sure that it is still alive. If the target does not respond within 5
seconds, it will power cycle the box instead of issuing a reboot.

Five seconds may be too short, and ktest may unnecessarially power cycle the
box. I have found 25 seconds seems to be a better timeout for this purpose.
But even 25 may be too arbitrary. Add a CONNECT_TIMEOUT option to let the
user determine the timeout time before rebooting. By default, it has been
raised to 25 seconds.

Signed-off-by: Steven Rostedt (VMware) <rostedt@goodmis.org>