[libvirt] [PATCH] Unify pool-create-as and pool-define-as xml building

The attached patch unifies the xml building and command line option registering for the virsh pool-*-as commands, fixing a few bugs in the process: - pool-define-as was creating <host> without a name attribute (rhbz 476708) - pool-create-as wasn't adding a closing tag to its <host> block - pool-create-as didn't have the source-name option All seem like a good justification for not duplicating the logic. The patch ends up looking a bit bizarre, but it's mostly just moving the xml building from create-as into a separate function buildPoolXML, and then wiring it up. Thanks, Cole