Ability to pass environment variables

[karencfv]

It would be really nice to have the ability to pass environment variables to the packages we're building. This will be specifically helpful when wanting to deploy for different environment types during the development cycle.

For example, today some of our smf directories sometimes have several configuration subdirectories. Instead of having several copies of the same config file with different values, it'd be really nice to be able to set these values as environment variables at build time