ktest: Rewrite the config-bisect to actually work

I never liked the way config-bisect worked. I would assume the bad config
had some config that broke the system. But it would not work if the bad
config just happened to be missing something that the good config had.

I rewrote the config-bisect to do this properly. It does a diff of the two
configs, and sets half of the configs that are in one and not the other.
The way it works is that when it "sets", it really just makes one copy
what the other has. That is, a "set" can be setting a:

  # CONFIG_FOO is not set

Basically, it looks at the differences between the two files and makes
them similar until it comes down to one config that makes it work or
not work depending on if it is set or not.

Note, if more than one config change makes the bad config not work, it
will only find one of them. But this is true with all bisect logic.

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