Support for other Parallel Testing gems

[priverop]

Hello!

I've been trying to make simplecov working with parallel_rspec, an alternative to parallel_test, but if I'm not mistaken, this is highly acoplated because of this require and probably other functions.

I thought that if only the parallel_rspec gem would use ENV["TEST_ENV_NUMBER"] and ENV["PARALLEL_TEST_GROUPS"] I could make it work, but apparently it's not that simple.

Am I mistaken? It would be a difficult task? Do you think it would be useful to allow to use different gems?

Thank you!