Expose the JmxFeed builder created by JavaAppUtils connectMXBeanSensors

Allows entities to call getMxBeanSensorsBuilder and add further polls
without having to create a second JmxFeed. The existing behaviour of
connectMxBeanSensors is unchanged. Deprecates `times` in favour of
the functions in brooklyn.util.math.MathFunctions.
Don't attempt to rebind to existing applications in BrooklynLauncherTest

Test was failing because I had persisted entities that were not on the
test's classpath.