Fix BrooklynAccessUtils for entities with multiple locs

- some entities have the provisioning-location and them machine-location
  added to them. So need to find the one SupportsPortForwarding,
  rather than assuming there will be exactly one location
Adds LoadBalancer.HOST_AND_PORT_SENSOR

- For a single sensor that gives host:port
  This is particularly useful when transforming sensor values,
  e.g. in port-mappings, where we want to convert a port the the
  host:port that it can be accessed on.
Fix time-sensitive AbstractGeoDnsServiceTest
Improve err messages in EntityTestUtils