HotRodServerConfigurationBuilder.build() mutates the builder

When HotRodServerConfigurationBuilder.build() calls validate(), and proxyHost/proxyPort is not set, it sets its value. That causes problems if you call build() once, (throw away the configuration) and reset host/port to different value - proxyHost/proxyPort is already set, although the user thinks that it's at its defaults (the same as host/port).