Re: [libvirt] PATCH: Only pass in emulator if user requested it

Previouly with Xen we would only specify an emulator path to XenD if there was one provided in the XML. With the new domain XML routines we will always lookup the default emulator path internally using our capabilities data. So XenD sees an explicit emulator path even if the user didn't request one. This works fine, except for paravirt guests where you only want to have the text console active, and not the graphical framebuffer. In this scenario, XenD starts QEMU-DM to handle the text console, but it crashes because PVFB isn't configured. This patch switches us back to the old behaviour where we only pass an emulator to XenD if the user actually specified one - XenD is intelligent enough to auto-configure a QEMU instance for paravirt framebuffers as needed. The logic looking up the default emulator did live in the generic XML parsing routines. This patch removes it from the XML parsing stage, and pushes it down into the individual drivers at time of use (if they so desire).