make libparted poke the kernel when adding/deleting partitions

make libparted poke the kernel when adding/deleting partitions

Turns out that libparted is already using the right ioctl's mentioned
in commit 6a2a1f2b7cc7b52b277aa9788a3a0bb280227441. So now we can
correctly add/delete partitions even when other partitions on the same
disk are busy.