[SPARK-1041] ec2-related lines in start-*.sh no longer work

https://spark-project.atlassian.net/browse/SPARK-1041?jql=project%20%3D%20SPARK

a.  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 IP, (in Oregon region), like ubuntu@ip-172-31-32-76:....

b. 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 "

c. the IP parameter in JettyUtils.startJettyServer is actually not used