Adds a version constant for it, bwc indices, and a vagrant upgrade-from
version. Also bumps the "upgrade from" version for the backwards-5.0
test and adds `skip`s for tests that don't fail against 5.0 so we skip
them during the backwards testing.
Finally, this skips the "Shrink index via API" test because it fails
consistently for me. Inconsistently for CI, but consistently for me.
I'll work on making it consistent tomorrow.
Nik Everett