Support for device classes feature in ceph deployment

Luminous adds a new property to each OSD: the device class. CRUSH rules can restrict placement to a specific device class.

To support device class features, we need to do two things:

1. Support for configuring osd device class, because osd in kolla is re-configured crush map after bootstrap, so there is no default device class. In kolla-ansible, we can configure device class in node units.
2. Support to specify the device class when creating a pool. For erasure pool, just specify the erasure profile name, ceph will automatically generate the corresponding crush rule name which is the same as the pool name.