Support different rexml location for older vagrant (#1493)
Support different rexml location for older vagrant (#1493)

Attempt fallback to loading rexml from rexml/rexml which is the path
used by older vagrant releases.

Fixes #1483
vagrant-libvirt/vagrant-libvirt,electrofelix/vagrant-libvirt,vagrant-libvirt/vagrant-libvirt,vagrant-libvirt/vagrant-libvirt,electrofelix/vagrant-libvirt,electrofelix/vagrant-libvirt