Better container support

[jcoffland]

The following features would help with running v8 fah-client in a container:

• exit-when-done: option to run one set of WUs then exit.
• enable-all-gpus: Default all GPUs to enabled.
• fold-at-start: Start folding automatically.

However, note that since containers can be configured to automatically join an account using the account-token option, they can easily be controlled remotely.