Zero-downtime deploy - configurable wait time for green status

This pull request adds a --wait-time option to zdt_deploy to set the number of seconds the script waits for the environment to become green. 

The default is 600 seconds; we are using the script to deploy Docker applications, and since the docker deploy pulls large filesystem layers from a remote Docker repo, the wait time needs to be a few more minutes. This change addresses that by letting the user specify the number of seconds to wait.