For crash testing: kill the server without generating core file.

include/my_dbug.h
  Use kill(getpid(), SIGKILL) which cannot be caught by signal handlers.
  All DBUG_XXX macros should be no-ops in optimized mode, do that for DBUG_ABORT as well.
sql/handler.cc
  Kill server without generating core.
sql/log.cc
  Kill server without generating core.