Add .travis.yml file for Travis CI
Use SPARK_HOME to find `run` in DriverSuite.
Display unit-tests.log after failed Travis build
Replace Typesafe repository with Akka repo.
Enable verbose logging in Travis unit tests.
Enable verbose logging in all unit tests.

This is a short-term debugging aid until I figure out how to properly use
a different log4j.properties file when running under Travis.