ktest: Allow overriding bisect test results

When running the ktest git bisect test, if the BISECT_TYPE is "test",
the bisect is determined to be good or bad based off of the error
code of the test that is run. Currently, if the test returns 0,
it is considered a pass (good), a non-zero is considered a fail (bad).

But it has been requested to add more options, and also change
the meanings of the error codes of the test. For example, one may
want the test to detect if the commit is not good or bad,
(maybe the bisect came to a point where the code in question
does not exist). The test could report an error code that should tell
ktest to skip the commit.

Also, a test could detect that something is horribly wrong and the
biscet should just be aborted.

The new options:

 BISECT_RET_GOOD
 BISECT_RET_BAD
 BISECT_RET_SKIP
 BISECT_RET_ABORT
 BISECT_RET_DEFAULT

have been added. The first 4 take an integer value that will
represent if the test should be considered a pass, fail, neither
good nor bad, or abort respectively.

The BISECT_RET_DEFAULT will bo whatever is not defined by the
above codes. If only BISECT_RET_DEFAULT is defined, then all tests
will do the default.

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