Migrating reactor_ev to subtests.

[sergiotarxz]

Summary

Migrating reactor_ev.t to subtests.

I have tried to split the tests to use their own variables but I was not able for most of them, I am creating this pull request to see if it can fit like it is and if not to attempt to get advice to do it better.

Motivation

Issue #1520

References

#1520

[kraih]

For reviewers, hiding whitespace changes makes these PRs a lot easier to review.