Exposes JavaAppUtils' JmxFeed builder and fixes test in BrooklynLauncherTest

Usage:
```
jmxFeed = JavaAppUtils.getMxBeanSensorsBuilder(this)
                .pollAttribute(new JmxAttributePollConfig<Boolean>(SENSOR)
                        .objectName(MBEAN_NAME)
                        .attributeName("Name"))
                .build();
```