This should be env, not env2
Handle config.vm.box_url

Beause ConfigValidate checks options that may be provided by an AWS box,
we need to call BoxHandleUrl before ConfigValidate.
Merge pull request #64 from psi/handle-box-url

Handle config.vm.box_url
Merge branch 'master' of github.com:mitchellh/vagrant-aws
release elastic ip address upon termination