qemu: rework '-serial none'
qemu: rework '-serial none'

Limiting ourselves to qemu without QEMU_CAPS_DEVICE capability, we
used '-serial none' only if there was no serial device defined in the
domain XML.  This means that if we want to have a possibility of the
device being defined in XML, but not used in the command-line
(e.g. when it's pointless), we'll fail to attach '-serial none' to the
command-line (when skipping the device's command-line building and the
device being the only one).

Since there is no such device, this patch doesn't actually do
anything, but enables easier future additions in this manner.

Signed-off-by: Martin Kletzander <e82f23e74d43760279ebcc505dac4ae70d5627d0@redhat.com>

jardasgit/libvirt,crobinso/libvirt,fabianfreyer/libvirt,jfehlig/libvirt,andreabolognani/libvirt,jfehlig/libvirt,andreabolognani/libvirt,VenkatDatta/libvirt,jfehlig/libvirt,olafhering/libvirt,datto/libvirt,rlaager/libvirt,taget/libvirt,agx/libvirt,datto/libvirt,zippy2/libvirt,elmarco/libvirt,jardasgit/libvirt,taget/libvirt,eskultety/libvirt,jardasgit/libvirt,nertpinx/libvirt,VenkatDatta/libvirt,taget/libvirt,rlaager/libvirt,VenkatDatta/libvirt,olafhering/libvirt,agx/libvirt,shugaoye/libvirt,crobinso/libvirt,zippy2/libvirt,crobinso/libvirt,rlaager/libvirt,taget/libvirt,datto/libvirt,datto/libvirt,olafhering/libvirt,elmarco/libvirt,jfehlig/libvirt,crobinso/libvirt,shugaoye/libvirt,libvirt/libvirt,shugaoye/libvirt,libvirt/libvirt,elmarco/libvirt,eskultety/libvirt,zippy2/libvirt,nertpinx/libvirt,andreabolognani/libvirt,elmarco/libvirt,taget/libvirt,VenkatDatta/libvirt,agx/libvirt,nertpinx/libvirt,jardasgit/libvirt,fabianfreyer/libvirt,shugaoye/libvirt,andreabolognani/libvirt,datto/libvirt,rlaager/libvirt,eskultety/libvirt,nertpinx/libvirt,fabianfreyer/libvirt,eskultety/libvirt,agx/libvirt,olafhering/libvirt,libvirt/libvirt,elmarco/libvirt,nertpinx/libvirt,shugaoye/libvirt,libvirt/libvirt,fabianfreyer/libvirt,eskultety/libvirt,jardasgit/libvirt,andreabolognani/libvirt,fabianfreyer/libvirt,rlaager/libvirt,agx/libvirt,zippy2/libvirt,VenkatDatta/libvirt