Tomcat should support the java interface

If you have a charm that depends on Tomcat, and that charm uses Java, you can run into issues with the hostname being too long for Java 7 on LXD and GCE.

I ran into this specifically when taking a look at the Saiku charm in the review queue (https://code.launchpad.net/~spicule/charms/trusty/saikuanalytics-enterprise/trunk), which fails, after fetching the trial license, with a Java exception related to the hostname.

The downside is that any charms that currently rely on Tomcat would need to setup a relation to openjdk. The upside is that the charms will work consistently across Clouds ...

The relevant Java Exception, for reference: http://paste.ubuntu.com/16230171/