refactor(listener) refactor listener related code
Remove duplicate code around creating http listener.
Start to listen incoming http requests just before serving them.
Merge pull request #626 from xiangli-cmu/refactor_listener

refactor(listener) refactor listener related code
fix(server/transporter.go) fix the short timeout problem of sending snapshot
Snapshot can be tens of MB. We need to have a minute level timeout for sending snapshot.
We add a separate snapshot http client for snapshot request, which has 120s timeout.
docs(api): updated examples and description of CAS and CAD
chore(Vagrantfile): Add Vagrant file for easy start
Merge branch 'master' of https://github.com/coreos/etcd