8265690: Use the latest Ubuntu base image version in Docker testing

Reviewed-by: sgehwolf, iignatyev, mseledtsov

test/lib/jdk/test/lib/containers/docker/DockerfileConfig.java

@@ -52,7 +52,7 @@ public class DockerfileConfig {
             case "s390x":
                 return "s390x/ubuntu";
             default:
-                return "oraclelinux";
+                return "ubuntu";
         }
     }
 
@@ -63,13 +63,6 @@ public class DockerfileConfig {
             return version;
         }
 
-        switch (Platform.getOsArch()) {
+        return "latest";
-            case "aarch64":
-            case "ppc64le":
-            case "s390x":
-                return "latest";
-            default:
-                return "7.6";
-        }
     }
 }