Reduce memory usage by OSDs during peering

Memory usage is linear to the number of placement groups (PGs) hosted on the particular object storage device (OSD), but another factor can consume memory during peering- the number of OSD maps needed to go through during peering. In some situations, such as an OSD is out for a long period of time, peering as the OSD maps are iterated can consume large amounts of memory and result in poor perf...