improve remote tests

see: https://github.com/bazelbuild/rules_scala/pull/83

we need to have tests that verify that the rules work when using targets in remote repos. The testing is not clear there.

I think we need to set up two test WORKSPACES:
1) depends on the rules and defines some thrift/scala targets.
2) second repo depends on the first, and consumes some thrift classes from the target in 1.

Start by reading the linked pull request #83 and reviewing how remote-repository tests are currently organized. Set up the two test WORKSPACES described in the issue: one defining Thrift/Scala targets using the rules, and another depending on it and consuming generated Thrift classes. Done means the tests verify rule behavior across those remote repository boundaries.

Written by the indexing model from the issue text.