MessageSource logs at WARN level on every message

[snicoll]

When boot uses spring-boot-starter-security (or simply spring-security) the following warning is emitted

WARN 35370 --- [nio-8080-exec-1] o.s.c.s.ResourceBundleMessageSource      : ResourceBundle [messages] not found for MessageSource: Can't find bundle for base name messages, locale en_US

Tracking that to AbstractUserDetailsAuthenticationProvider#authenticate

@rwinch, thoughts?

I have this with a plain execute of the main method of the boot application in the IDE so this happens without the executable jar

[dsyer]

It's really the MessageSourceAutoConfiguration that's the culprit. We probably should suppress it somehow if the MessageSource cannot resolve a resource bundle.