Improve Tester Shutdown

[ro-tex]

Note: This also needs to happen in accounts.

f/u This is not very graceful because the goroutines might just be terminated when the test ends without making sure the http server actually shut down. One way to do that gracefully is something like this

tester.externShutdownDone = make(chan error)
go func() {
  tester.externShutdownErr = srv.ListenAndServe()
  close(tester.externShutdownDone)
}()

and then

func (t *Tester) Close() error {
  if err := t.staticSRV.Shutdown(someCtx); err != nil {
    return err
  }
  <-tester.externShutdownDone
  return tester.externShutdownErr
}

Originally posted by @ChrisSchinnerl in #1 (comment)