Currently paths to certificates used in the test suite are defined in both SpecConfig and globally in lite spec helper. The global definition is the legacy one; the issue with it is it is not usable from, for example, the spec:prepare rake task. We should consolidate the definitions in SpecConfig, taking into account the environment variables set by drivers-evergreen-tools.

As part of this work the duality between using cert directory and hard coding file names within it / having per-file accessor methods should also be resolved.