busybox: update test case du-k-works

busybox: update test case du-k-works

busybox test case du-k-work fails on ext3/4 image whose size less than
512M. Add patch testsuite-du-du-k-works-fix-false-positive.patch to fix
it and it has been merged by upstream.

[Yocto 2896]

(From OE-Core rev: ffe4f8a859d5e71e3e33363d61f0470a32c48d66)

(From OE-Core rev: 19eb2971c6e8c4a2847897919ec7a2cd9b1697b1)

Signed-off-by: Kang Kai <kai.kang@windriver.com>
Signed-off-by: Saul Wold <sgw@linux.intel.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>