Demote WARN to INFO if behaviour is expected for connect. (#1211)

In the register phase connecting to Elasticsearch does not warrant a WARN as it is expected behaviour.

This commit moves the log entry from WARN to INFO to cut down on logging, and differentiates the text message accordingly.

Author: ash-darin

lib/logstash/outputs/elasticsearch/http_client/pool.rb

@@ -286,7 +286,11 @@ def healthcheck!(register_phase = true)
           raise root_bad_code_err if root_bad_code_err
 
           # If no exception was raised it must have succeeded!
-          logger.warn("Restored connection to ES instance", url: url.sanitized.to_s)
+          if register_phase
+            logger.info("Connected to ES instance", url: url.sanitized.to_s)
+          else
+            logger.warn("Restored connection to ES instance", url: url.sanitized.to_s)
+          end
 
           # We check its ES version
           es_version, build_flavor = parse_es_version(root_response)