Add abort method to TinMan/Oz plugin

This depends upon some internal details of the Oz guest objects

Oz intentionally does not expose libvirt domain objects as instance variables.
They are kept as local variables and passed around.

It might be worth asking Chris to add an abort() method directly into the Oz
Guest class.
Merge pull request #309 from aeolusproject/feature/oz_abort_merge

Add abort method to TinMan/Oz plugin