ceph-disk: bluestore list

ceph-disk: bluestore list

The objectstore journal and the bluestore block auxiliary device are
handled in the same way. Each occurrence of journal in the code is
replaced with a variable.

A few helpers are added to the Ptype class to factorize the most common
lookups but the code logic is unmodified with one exception: the
more_osd_info previously added a journal_uuid entry regarless. If there
was no journal_uuid file, it would be None. It is changed to only add
the {block,journal}_uuid entry if the corresponding file exist.

Signed-off-by: Loic Dachary <loic@dachary.org>