Create deployment container

[ddohler]

Most of the deployment dependencies are encapsulated in https://github.com/azavea/cac-tripplanner/blob/develop/python/cac_tripplanner/deployment_requirements.txt , but building AMIs also relies on Packer, which is not a Python dependency, and therefore isn't included when installing dependencies from this file. We should create a deployment container that contains both Packer and the Python deployment dependencies so that developers can deploy the application without having Packer installed locally.