Introduce create_cargo_factory to share code for the linux and mac cargo builders.
Introduce create_cargo_factory to share code for the linux and mac cargo builders.

ALikhachev/saltfs,UK992/saltfs,ALikhachev/saltfs,setupminimal/saltfs,servo/saltfs,rwaweber/saltfs,setupminimal/saltfs,setupminimal/saltfs,servo/saltfs,rwaweber/saltfs,rwaweber/saltfs,UK992/saltfs,UK992/saltfs,ALikhachev/saltfs