[libvirt] Add support for legacy -vmchannel option
These patches add support for the legacy qemu -vmchannel option. The following
domain xml:
<channel type='unix'>
<source mode='bind' path='/tmp/vmchannel'/>
<target type='vmchannel' deviceid='0200'/>
</channel>
becomes:
-vmchannel di:0200,unix:/tmp/vmchannel,server,nowait
I don't expect these to be merged, but I would appreciate a review.
Thanks,
Matt