Move read_log() function to prep for next commit

Signed-off-by: David Zafman <david.zafman@inktank.com>
Reviewed-by: Samuel Just <sam.just@inktank.com>
osd: create tool to extract pg info and pg log from filestore

New application ceph-filestore-dump created that mounts filstore
and can dump info or log in JSON when an OSD is not running.

Feature: #3890

Signed-off-by: David Zafman <david.zafman@inktank.com>
Reviewed-by: Samuel Just <sam.just@inktank.com>
doc: v0.56.2 release notes

Signed-off-by: Sage Weil <sage@inktank.com>
Merge git://github.com/ceph/ceph