Enumerate Ceph OSD partitions with multi-digit index

When there's more than 6 OSDs per OSD Journal device, some OSD journal
partitions end up having double-digit partition index number. This patch
modifies the ls command used to enumerate journal partitions to account for
that multi-digit partition index numbers.

Change-Id: I654b5c070324887f9ffd41e6eb5e231851b97404
Closes-Bug: #1339833