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.