`g8Test` uses other code path than actual template application

It seems that `g8Test` uses another code path than actually using the command line tool or `sbt new` to apply a template. With the tool / `sbt new` template generation can fail fatally for issues like #333. Using `g8Test` it works because there's a fallback defined that falls back to copying the template verbatim if actually running the ST template fails. That makes it really hard to test template generation in CI.

It seems the difference is in using `G8.applyT` version `G8.apply`.

Observed here: https://github.com/akka/akka-http-quickstart-scala.g8/issues/15