SPARK-4159 [CORE] Maven build doesn't run JUnit test suites

This PR:

- Reenables `surefire`, and copies config from `scalatest` (which is itself an old fork of `surefire`, so similar)
- Tells `surefire` to test only Java tests
- Enables `surefire` and `scalatest` for all children, and in turn eliminates some duplication.

For me this causes the Scala and Java tests to be run once each, it seems, as desired. It doesn't affect the SBT build but works for Maven. I still need to verify that all of the Scala tests and Java tests are being run.
It looks like this particular `<execution>` configuration is specific to the `java8-tests` submodule; do we need to preserve this logic?