Detect whether we run on EC2 using ec2-metadata as well
Merge pull request #419 from shivaram/ec2-ip-change

Detect whether we run on EC2 using ec2-metadata as well
Track workers by executor ID instead of hostname to allow multiple
executors per machine and remove the need for multiple IP addresses in
unit tests.
Rename more things from slave to executor
Clean up BlockManagerUI a little (make it not be an object, merge with
Directives, and bind to a random port)
Merge branch 'mesos'