ktest: Reboot after each patchcheck run

The patches being checked may not leave the kernel in a state
that the next run will allow the new kernel to be copied to the
machine. Reboot to a known good kernel before continuing to the
next kernel to test.

Added option PATCHCHECK_SLEEP_TIME for the max time to sleep between
patchcheck reboots.

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