HDFS-10831. Add log when URLConnectionFactory.openConnection failed. Contributed by yunjiong zhao.

(cherry picked from commit b07c266dca7f303c793b432a0738d593728cf2b3)
(cherry picked from commit 72ea64146810bb5010280145ee7cad9fb9375aad)

hadoop-hdfs-project/hadoop-hdfs-client/src/main/java/org/apache/hadoop/hdfs/web/URLConnectionFactory.java

@@ -183,6 +183,7 @@ public class URLConnectionFactory {
       return openConnection(url, false);
     } catch (AuthenticationException e) {
       // Unreachable
+      LOG.error("Open connection {} failed", url, e);
       return null;
     }
   }