Merge pull request #431 from maseev/issue430

Added docker container format

Author: gondor

core/src/main/java/org/openstack4j/model/image/ContainerFormat.java

@@ -40,6 +40,11 @@ public enum ContainerFormat {
 	 */
 	AMI,
 
+	/**
+	 * This is the Docker container format
+	 * */
+	DOCKER,
+
 	/**
 	 * Type unknown
 	 */