[compute] Add update_image_metadata request

lib/aviator/openstack/compute/v2/public/update_image_metadata.rb

@@ -0,0 +1,38 @@
+module Aviator
+
+  define_request :update_image_metadata, inherit: [:openstack, :common, :v2, :public, :base] do
+
+    meta :service, :compute
+
+    link 'documentation',
+         'http://docs.openstack.org/api/openstack-compute/2/content/Update_Metadata-d1e5208.html'
+
+
+    param :id,       required: true
+    param :metadata, required: true
+
+
+    def body
+      {
+        metadata: params[:metadata]
+      }
+    end
+
+
+    def headers
+      super
+    end
+
+
+    def http_method
+      :post
+    end
+
+
+    def url
+      "#{ base_url }/images/#{ params[:id] }/metadata"
+    end
+
+  end
+
+end