ktest: Detect typos in option names

It becomes quite annoying when you go to run a test and then
realize that you typed an option name wrong, and the test starts
doing the default action and not what you expected it to do.

It is even more annoying when you wake up the next day after
running the test over night when you discover this.

By testing if all options specified in a config file are
used by either ktest or were used in one of the option's values
we can see if there are any dangling options that were not used.
In such a case, show the user the options that were not used
and ask them if they want to continue or not.

The option IGNORE_UNUSED was also added to allow the user to
override this feature.

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