ktest: Fix make_min_config test when build fails

The make_min_config does not take into account when the build fails,
resulting in a invalid MIN_CONFIG .config file. When the build fails,
it is ignored and the boot test is executed, using the previous built
kernel. The configs that should be tested are not tested and they may
be added or removed depending on the result of the last kernel that
succeeded to be built.

If the build fails, mark the current config as a failure and the
configs that were disabled may still be needed.

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