Merge rvm-test inside the rvm repository

[eregon]

Description

Currently, the RVM test suite is a separate repository: https://github.com/rvm/rvm-test

It is imported as a git submodule.
Git submodule are to say the least inconvenient to work with.

As such, I proposed to merge rvm-test in rvm, since I don't think it's very valuable to have its own repository, and it's quite inconvenient to fix a bug and add a test:
3 PRs (rvm, rvm-test, bump import in rvm) to 2 different repos instead of just one PR to one repo.

cc @pkuczynski @mpapis

[eregon]

Also, the CI of rvm-test is redundant with rvm's, and not in sync, so it's not possible to introduce a new test without the fix being merged in rvm first, and there are probably more synchronization issues.

[eregon]

e.g., the CI of rvm-test is broken on rvm/rvm-test#27, but it doesn't matter since the important one is rvm's CI.

[pkuczynski]

I agree. I think the only reason why those are not included is to make the bundle smaller, but the hassle is not worth it I think. @mpapis?

[eregon]

@mpapis gentle ping 😃

[eregon]

This was done in 7930978 / #4757 as a git subtree, thanks @mpapis!