Add ability to export env variables through salt

[burntcarrot]

Scope/Type: config

Related discussion here.

I think that salt should have the ability to export environment variables and their respective values through a helper function; the closest we can get as of now is through the getFlattenedStructKeys function, which allows us to get keys. (which is private in nature, as it is an utility function)

It could be helpful in situations like this, where we need to get env vars. (salt could help in exporting values (more specifically, env variable key-value pair) into a map[string]string, which can then be used in populateData in meteor.)