Unit tests require de430.bsp kernel for testing

[medley56]

The de430.bsp kernel appeares to be required for some of the unit tests and is expected to be in data/generic. I suspect this is a large kernel and that's why it wasn't committed but we should either

1. mock out the need for this kernel (probably unlikely)
2. commit it despite its size (we could use LFS), or
3. dynamically fetch/cache it from NAIF when it's needed.

[medley56]

I see that the Dockerfile is pulling this in from NAIF for Dockerized testing. Could we do a similar thing using a pytest fixture so it's not dependent on running in Docker?