New e2e script (in go this time) that doesn't completely suck

Will continue to expand scripts like this while shrinking the bash scripts over time. This is a good first step, it's not completely impossible to use like the script it replaces was.
Danger, danger.  Comma is a valid file name character.  Are you planning to unescape that?

I think simpler is better here.  If someone is changing the tests argument it is probably because they want to run a single test, anyway.