ceph-disk: retry on OSError

ceph-disk: retry on OSError

we are likely to
1) create partition, for instance, sdc1
2) partprobe sdc
3) udevadm settle
4) check the device by its path: /dev/sdc1

but there is chance that the uevent sent from kernel fails to reach udev
before we call "udevadm", hence "/dev/sdc1" does not exist even after
"udevadm settle" returns. so we retry in case of OSError here.

Signed-off-by: Kefu Chai <kchai@redhat.com>