Ceph: adjust ceph.conf settings for v0.65

v0.63 changed ‘osd min down {reporters|reports}' 'mon osd min down
{reporters|reports}' per our bug report, change our config to prepare
for that. Also remove 'osd min pg log entries' as it was a workaround
for #5084 which could be fixed now.

Change-Id: Id66e297925a28fa0589a0f3b4b9ad8f445c73b54