Allow use of image (typically logan-terraform)

• Adds support for image entry in configuration file specifying which image to run the command in.
• Allows prevention of pull every time with --nopull argument (similar to --nobuild).
• Additional environment variables can be specified in the config file to be passed in to the container (useful for overriding TERRAFORM_KUBECONFIG_OUTPUT used by with-kubeconfig.sh wrapper)
• up'ed version

Closes: #1 (closed)