2htdp/universe tests: use distinct port numbers

Using distinct port numbers allows the tests to run concurrently.
Using locally distnct port numbers is not a general solution,
of course, but it should work well enough for running these
tests with `raco test --drdr`.
raco test: refine override-"info.rkt" behavior of specifying a file

In consultation with Jay, unify the ignore-file's-extension and
ignore-"info.rkt"-disabling treatment of `raco test` arguments.
The change is that the latter applies only when an argument is a
file, and not when it's a directory.