ktest: Add poweroff after halt and powercycle after reboot

Added the options POWEROFF_AFTER_HALT to handle boxes that do not
really shut off after a halt is called.

Added POWERCYCLE_AFTER_REBOOT to force a power cycle for boxes that
don't reboot but get stuck during the reboot.

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