Ceph: CPU and RAM resources

Ceph requires at least

* 0.5 physical cores per OSD for spinning, 2 cores per SSD OSD;
* 1GB of RAM per 1TB of OSD storage, minimum 2GB (for example, a 900GB drive would spec 2GB of RAM, a 4TB drive would recommend 4GB of RAM).

These requirements become strict when OSDs are deployed on same node, as nova-compute. Minimal amount of resources should be guarantee using CPU affinity and cgroups for RAM, or with other techniques. There are also two settings in Nova we can use to control this: 'vcpu_pin_set', which lets you control which physical CPUs that VCPUs can use, and 'reserved_host_memory_mbm', which will remove some amount of memory from the hypervisor's resource calculations.