Implement Linux kernel configuration bisection. Use bisected minimalistic
configuration in commit bisection. Utilizes config_bisect.pl script from Linux
kernel tree in bisection.
Modify syz-bisect to read in kernel.baseline_config. This is used as a "good"
configuration when bisection is run.
1. Filename should be relative to flagCrash, not the current dir.
2. Use osutil.IsExist, os.Stat can fail for other reasons, e.g. no permissions.
3. Dedup filepresence check.
Detect bisection to merge commits and to commits that don't affect
kernel binary (comments, other arches, whitespaces, etc).
Such bisections are not reported in emails (but shown on web).
Update #1271
* Modify Run() to return the commit object when a failure occurs on the
oldest tested release(for BisectCause) and latest tested
release(for BisectFix).
* Modify tests to check the returned commit object.
A bunch of improvements after more wide bisection testing.
Improve logging.
Support returning several commits for inconclusive bisection.
Return Report with the final crash.
Remove code that was moved to pkg/vcs.
Update #501
mgrconfig was used only by syz-manager initially,
but now it's used by a dozen of packages and it's
weird to import from under a binary dir.
pkg/ is much more reasonable dir for a widely used
helper package.
