parted: use update-alternatives for partprobe

parted: use update-alternatives for partprobe

busybox may also provide a partprobe implementation, so use u-a to allow
installing them side by side.
If one installs both, busybox and parted, one gets the following error:

| ERROR: image do_rootfs: Postinstall scriptlets of ['busybox'] have failed. If the intention is to defer them to first boot,
| then please place them into pkg_postinst_ontarget_${PN} ().
| Deferring to first boot via 'exit 1' is no longer supported.

And the coresponding log.do_rootfs extract:

| ...
| update-alternatives: Error: not linking ...image/rootfs/usr/sbin/partprobe to /bin/busybox.nosuid since ...image/rootfs/usr/sbin/partprobe exists and is not a link
| ...

(From OE-Core rev: 99b74d1ff23ef91c84dc81ecf6437ad3bc37fb64)

Signed-off-by: Max Krummenacher <max.krummenacher@toradex.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>