Log test execution start and end

CI jobs hang regularly, this could help to tell whether
the cause is the tests themselves or something in the CI
environment.

(cherry picked from commit 8d9f1ff)

Author: acogoluegnes

src/test/resources/logback-test.xml

@@ -5,6 +5,8 @@
         </encoder>
     </appender>
 
+    <logger name="com.rabbitmq.client.test.BrokerTestCase" level="info" />
+
     <root level="warn">
         <appender-ref ref="STDOUT" />
     </root>