Refactor Scala specs

- larger coverage
- easier maintenance (less repetitions)
Scala: export SBT_OPTS and JVM_OPTS for sbt builds

Related to travis-ci/travis-cookbooks#234
Cleanup: use 'do...end' blocks instead of '{...}'
Merge pull request #154 from gildegoma/paulp-sbt-extras

Scala/sbt: Export SBT_OPTS and JVM_OPTS