Start WorkerUI server on public address

1.  the assumption that the hostname of ec2 instances always starts with "ec2-internal" is not right now

e.g. the instance is identified by its internal, (in Oregon region), like ubuntu@ip-172-31-32-76:....

2. the Restful URI to get public hostname is changed in AWS, now, we should do something like 

wget -q -O - http://169.254.169.254/latest/meta-data/public-hostname 

3. the IP parameter in JettyUtils.startJettyServer is actually not used