ktest: Add timeout for ssh sync testing

Before rebooting the box, a "ssh sync" is called to the test machine to see
if it is alive or not. But if the test machine is in a partial state, that
ssh may never actually finish, and the ktest test hangs.

Add a 10 second timeout to the sync test, which will fail after 10 seconds
and then cause the test to reboot the test machine.

Cc: stable@vger.kernel.org
Fixes: 6474ace9 ("ktest.pl: Powercycle the box on reboot if no connection can be made")
Signed-off-by: Steven Rostedt (VMware) <rostedt@goodmis.org>