[compute] Add get_server_metadata_item request

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

@@ -0,0 +1,31 @@
+module Aviator
+
+  define_request :get_server_metadata_item, inherit: [:openstack, :common, :v2, :public, :base] do
+
+    meta :service, :compute
+
+    link 'documentation',
+         'http://docs.openstack.org/api/openstack-compute/2/content/Get_Metadata_Item-d1e5507.html'
+
+
+    param :id,  required: true
+    param :key, required: true
+
+
+    def headers
+      super
+    end
+
+
+    def http_method
+      :get
+    end
+
+
+    def url
+      "#{ base_url }/servers/#{ params[:id] }/metadata/#{ params[:key] }"
+    end
+
+  end
+
+end