osd: move pg log and info to a per-pg object

Move all PG metadata (info, biginfo, epoch, and log) to a single per-PG
object.  This should make it easier for ObjectStore implementations to
avoid lock contention in the write path.

Signed-off-by: Sage Weil <sage@redhat.com>
test/osd/osd-test-helper.sh: enable filestore log

Signed-off-by: Sage Weil <sage@redhat.com>
ceph_objectstore_tool: skip pgmeta objects in 'list' command

Signed-off-by: Sage Weil <sage@redhat.com>
osd/PGLog: drop support for ancient logs

Assume that users have at least upgraded to dumpling first.

Signed-off-by: Sage Weil <sage@redhat.com>
osd: prevent upgrade from older than v7

Signed-off-by: Sage Weil <sage@redhat.com>
fix DBObjectMap ... DO NOT MERGE