ktest: Add manual bisect

For both git bisect and config bisect, if BISECT_MANUAL is set to 1,
then bisect will stop between iterations and ask the user for the
result. The actual result is ignored. This makes it possible to
use ktest.pl for bisecting configs and git and let the user examine
the results themselves and enter their own results.

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