ktest: New features: noclean, dodie, poweroff on error and success

Added dodie function to have a bit more control over die calls.

BUILD_NOCLEAN to not run make mrproper or remove .config.

POWEROFF_ON_{SUCCESS,ERROR} to turn off the power after tests.

Skip backtrace calls that were done by the backtrace tests.

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