Implement TOSCA Container capabilities

The Container capability, when included on a Node Type or Template definition, indicates that the node can act as a container for (or a host for) one or more other declared Node Types. The Container capability now has properties, most of which were part of Compute node properties earlier.

Example:
tosca.capabilities.Container:
  derived_from: tosca.capabilities.Root
  properties:
    num_cpus:
      type: integer
      required: false
      constraints:
        - greater_or_equal: 1
    cpu_frequency:
      type: scalar-unit.frequency
      required: false
      constraints:
        - greater_or_equal: 0.1 GHz
    disk_size:
      type: scalar-unit.size
      required: false
      constraints:
        - greater_or_equal: 0 MB
    mem_size:
      type: scalar-unit.size
      required: false
      constraints:
        - greater_or_equal: 0 MB