Add travis and vagrant, 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.)

Vagrant enables us to locally reproduce an environment very similar to
travis'.  To select a default provider, echo its name to
`.vagrant/provider`. The default is virtual box.

To always use vmware fusion (for example):
```
$ echo vmware_fusion > .vagrant/provider
```

When starting a virtual machine, one can select a platform with the
`PLATFORM` environment variable.  For example:

```
$ PLATFORM=cdh4.5.0 vagrant up
```
Turn off everything except cdh4.4.0 while I hack up the scripts.