Add `get_config_value()` which searches and returns a setting in a known order.
Add `get_config_value()` which searches and returns a setting in a known order.

1. In the virtual machines configuration
2. In the virtual machine's provider configuration
3. In the salt cloud configuration
4. Return the provided default

saltstack/salt,saltstack/salt,saltstack/salt,saltstack/salt,saltstack/salt