Do not fail build if javadoc has warnings

And use clean before creating distribution.

Author: acogoluegnes

Makefile

@@ -19,8 +19,8 @@ all: deps
 deps: $(DEPS_DIR)/rabbit
 	@:
 
-dist:
-	$(MVN) $(MVN_FLAGS) -DskipTests=true package javadoc:javadoc
+dist: clean
+	$(MVN) $(MVN_FLAGS) -DskipTests=true -Dmaven.javadoc.failOnError=false package javadoc:javadoc
 
 $(DEPS_DIR)/rabbit:
 	git clone https://github.com/rabbitmq/rabbitmq-server.git $@