Stringify libcompose datatypes' leaf values to avoid unmarshaling errors, even on somewhat incorrect input data: like using bools or numerics in labels.
Read files cloud-config.d in alphanumeric order, then cloud-config.yml
`ros config` writes to cloud-config.yml (and cloud-config.d/private.yml - only private keys)
Add (c *CloudConfig) Save() method, use it to save the changed config
Read and apply metadata as part of LoadConfig()
Simplify ros config export logic
