ceph-disk: add get_dev_name, path helpers

Signed-off-by: Sage Weil <sage@inktank.com>
ceph-disk: refactor list_[all_]partitions

Make these methods work in terms of device *names*, not paths, and fix up
the only direct list_partitions() caller to do the same.

Signed-off-by: Sage Weil <sage@inktank.com>
ceph-disk: use get_dev_name() helper throughout

This is more robust than the broken split trick.

Signed-off-by: Sage Weil <sage@inktank.com>
ceph-disk: reimplement is_partition() using /sys/block

Signed-off-by: Sage Weil <sage@inktank.com>
debug