This allows us to specify external journals for osds which can greatly
improve performance when the external journals are on the solid-state
drives.

The new lookup and startup methods fix the previous races we had
preventing osds from being created properly.

This retains the same functionality as before and is completely
compatible with the previous method and labels, however this does set
new labels for all new bootstrap OSDs. This was due to a limitation
in the length of the name of a GPT partition.

Closes-Bug: #1558853
DocImpact
Partially-Implements: blueprint ceph-improvements
Change-Id: I61fd10cb35c67dabc53bd82270f26909ef51fc38