Switch to public git urls in `.gitmodules`.

As explained at

http://docs.travis-ci.com/user/build-configuration/#Git-Submodules

..it is better to use public git urls instead of private (ssh-based)
ones.  This allows travis to check the submodules out without an ssh
private key.
Enable building with travis, use a build matrix to select platform.

Per the travis user documentation at
* http://docs.travis-ci.com/user/languages/java/
* http://docs.travis-ci.com/user/build-configuration/#The-Build-Matrix

..we enable several parallel builds using the latest cloudera CDH
versions supported by the latest bento (ebi 2.0.1).

All builds are run with Oracle JDK 7 (travis no longer offers JDK 6
since its End of Life.)