CURATOR-526: drop log level for message to debug

ZooKeeper is backwards compatible and accepts older config
string formats, albeit without dynamic configuration
support. Since the older format is acceptable, we should not
log at error when we see the older format and should
instead simply log at debug.

Author: Ammar Khaku <ammar.khaku@gmail.com>

Reviewers: Enrico Olivelli <eolivelli@apache.org>, Russell Bolles

Closes #382 from akhaku/dropLogLevel

curator-framework/src/main/java/org/apache/curator/framework/imps/EnsembleTracker.java

@@ -211,7 +211,7 @@ private void processConfigData(byte[] data) throws Exception
             }
             else
             {
-                log.error("Invalid config event received: {}", properties);
+                log.debug("Invalid config event received: {}", properties);
             }
         }
         else