osd: drop obsolete 'filestore' bool option

Signed-off-by: Sage Weil <sage@inktank.com>
os/ObjectStore: add static create() method

Generic way to create an ObjectStore implementation of the required type,
so that users don't need to know anything about it.

Signed-off-by: Sage Weil <sage@inktank.com>
osd: use ObjectStore::create() helper to create ObjectStore impl

No more knowledge of FileStore!

Signed-off-by: Sage Weil <sage@inktank.com>
osd: construct ObjectStore outside of OSD

This lets ceph_osd.cc handle the config details and use it directly for
all of the random command-line stuff, eliminating a bunch of mostly-
useless static wrappers in OSD.

Signed-off-by: Sage Weil <sage@inktank.com>
os/ObjectStore: generalize the FileStore's target_version

This kills the last FileStore reference in the OSD.

Signed-off-by: Sage Weil <sage@inktank.com>
osd: move peek_journal_fsid() into ObjectStore (from OSD)

This kills the last FileJournal reference in the OSD!

Signed-off-by: Sage Weil <sage@inktank.com>
os/ObjectStore: add {read,write}_meta

Move these from the OSD.  Use a generic implementation in ObjectStore that
hopefully all backends can share (so that it can remain in sync with the
start/stop scripts, ceph-disk, and other orchestration machinery).

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