Use maven to install OrientDB in travis

Rather than downloading the release from the OrientDB website, use maven instead as highlighted in this issue:

https://github.com/orientechnologies/orientdb/issues/2310#issuecomment-42178571

This means travis doesn't break when the orient website is down, download URLs change, limits are reached etc

hey @phpnode, thanks for the suggestion!

Im not superfamiliar with maven, could you try to do a first, initial, implementation of a PR?

Cheers!

@odino I copied the orientdb-odm CI config for my node.js client oriento, annoyingly the official release builds are not in maven, but the snapshots are, so I use a combination of the old technique of downloading from the website in some cases, and use maven for releases that aren't on the website yet. You can see my modifications here - https://github.com/codemix/oriento/tree/master/ci

One trick to avoid the download limits on the main site is to use the current git commit hash as part of the email address - https://github.com/codemix/oriento/blob/master/ci/odb-shared.sh#L48

thanks!