Use a quasi-unique group name in this e2e test.

[3405691582]

I suspect there may be either some lack of cleanup or race that occurs when executing the tests, since the error mentions "An instance group already exists with name: cvd". I don't want to plumb too deeply into figuring out exactly why this happens; instead, just generate a quasi-unique group name based on the time and this way they should likely not collide any more.