[FLINK-7046] [travis] Hide download logging messages

This closes #4226.

tools/travis_mvn_watchdog.sh

@@ -45,7 +45,8 @@ LOG4J_PROPERTIES=${HERE}/log4j-travis.properties
 
 # Maven command to run. We set the forkCount manually, because otherwise Maven sees too many cores
 # on the Travis VMs.
-MVN="mvn -Dflink.forkCount=2 -Dflink.forkCountTestPackage=1 -B -Dmaven.javadoc.skip=true $PROFILE -Dlog.dir=${ARTIFACTS_DIR} -Dlog4j.configuration=file://$LOG4J_PROPERTIES clean install"
+MVN_LOGGING_OPTIONS="-Dlog.dir=${ARTIFACTS_DIR} -Dlog4j.configuration=file://$LOG4J_PROPERTIES -Dorg.slf4j.simpleLogger.log.org.apache.maven.cli.transfer.Slf4jMavenTransferListener=warn"
+MVN="mvn -Dflink.forkCount=2 -Dflink.forkCountTestPackage=1 -Dmaven.javadoc.skip=true -B $PROFILE $MVN_LOGGING_OPTIONS clean install"
 
 MVN_PID="${ARTIFACTS_DIR}/watchdog.mvn.pid"
 MVN_EXIT="${ARTIFACTS_DIR}/watchdog.mvn.exit"