Add openstack client refactored api

[vmoravec]

Improvements:

• the openstackclient commands are DRY now
• command definition is more transparent
• add optional and mandatory (default) params
• add properties params
• add named params with property type

Example for openstack user command implementation:

      class User < Command
        self.command = "user"
        # commands like #delete, #show, #list are used from the parent
        def create name, options={}
          super do |params|
            params.add :optional, password: "--password"
            params.add :optional, email:    "--email"
            params.add :optional, project:  "--project"
            params.add :optional, enable:   "--enable",  param_type: :switch
            params.add :optional, disable:  "--disable", param_type: :switch
          end
        end

      end

Example for openstack.image command:

      class Image < Command
        self.command = "image"

        def create name, options={}
          super do |params|
            # mandatory params
            params.add container_format: "--container-format"
            params.add disk_format:      "--disk-format"

            # optional params
            params.add :optional, copy_from: "--copy-from"
            params.add :optional, location: "--location"
            params.add :optional, public: "--public", param_type: :switch
            params.add :optional, private: "--private", param_type: :switch

            # properties: will be transformed into --property hypervisor_type=kvm
            params.add :property, hypervisor_type: "hypervisor_type"
            params.add :property, vm_mode: "vm_mode"

            # fallback to all properties defined at once
            params.add :properties, param_type: :properties
          end
        end

      end

Additionally I added a method which tests existence of an asset without raising an exception (all the methods raise error e.g. deleting a non-existent user):

control_node.openstack.user.exist?("admin") # returns true or false