doc: Updated osd configuration reference.

Signed-off-by: John Wilkins <john.wilkins@inktank.com>
doc: Added a small ref section for osd config reference.

Signed-off-by: John Wilkins <john.wilkins@inktank.com>
doc: Added content to remove REJECT rules from iptables.

Signed-off-by: John Wilkins <john.wilkins@inktank.com>
doc: Added subnet example and verbiage to network settings.

fixes: #4049

Signed-off-by: John Wilkins <john.wilkins@inktank.com>
Merge git://github.com/ceph/ceph