Refactor Unit Tests

[jonathanio]

There could be some improvements around the handling of the unit tests. Including:

• Make foreign_option_* into an array: This will help with ordering, cleaning up after tests, and make it easier to work with and expand. Will need conversion out into the foreign_option_* variables however for internal processing, but will make the writing of tests easier and less error prone.
• dev could probably be random alongside the ifindex value: the script can never be configured for it, and it should never know it, and so to set it in the tests has no real purpose.
• Tests should only output in colour on colour-capable terminals.

[tomeon]

Done in #118.