Adding wait_until support for Elastic Beanstalk

[zabawaba99]

I'm currently deploying an application using the Elastic Beanstalk Client. However, I want my process to wait until the application is fully deployed ( the environment is in a 'ready' state ) and then check the version that is running.

It'd be great to have a wait_until method on the Client that would wait until an environment is in a 'ready' state.

[trevorrowe]

Thanks for the feature request. I've moved it over to the public backlog for the v2 SDK.