Change logging message and level for failed connection.

It is useful to get the reason for closing the connection.
For instance if connection was closed because the user is not
allowed to publish to the exchange.

Change-Id: I77ee5928618639baf19d8d5f60e25e3af3cc1f42

src/main/java/com/googlesource/gerrit/plugins/rabbitmq/session/type/AMQPSession.java

diff --git a/src/main/java/com/googlesource/gerrit/plugins/rabbitmq/session/type/AMQPSession.java b/src/main/java/com/googlesource/gerrit/plugins/rabbitmq/session/type/AMQPSession.java
index f7dfba6..437713e 100644
--- a/src/main/java/com/googlesource/gerrit/plugins/rabbitmq/session/type/AMQPSession.java
+++ b/src/main/java/com/googlesource/gerrit/plugins/rabbitmq/session/type/AMQPSession.java
@@ -58,9 +58,10 @@
           if (clazz == Channel.class) {
             Channel ch = Channel.class.cast(obj);
             if (cause.isInitiatedByApplication()) {
-              LOGGER.info(MSG("Channel #{} closed."), ch.getChannelNumber());
+              LOGGER.info(MSG("Channel #{} closed by application."), ch.getChannelNumber());
             } else {
-              LOGGER.info(MSG("Channel #{} suddenly closed."), ch.getChannelNumber());
+              LOGGER.warn(MSG("Channel #{} closed. Cause: {}"),
+                ch.getChannelNumber(), cause.getMessage());
             }
             if (ch.equals(AMQPSession.this.channel)) {
               AMQPSession.this.channel = null;