qemu: don't append -chardev arg until after value is formatted
qemu: don't append -chardev arg until after value is formatted

The act of formatting a chardev backend value may need to
append command line arguments for passing FDs. If we append
the -chardev arg before formatting the value, then the
resulting arguments will end up interspersed

Signed-off-by: Daniel P. Berrange <bb938cf255e055ff3507f2627d214e8e62118fcf@redhat.com>

jfehlig/libvirt,andreabolognani/libvirt,olafhering/libvirt,datto/libvirt,jardasgit/libvirt,eskultety/libvirt,nertpinx/libvirt,datto/libvirt,taget/libvirt,libvirt/libvirt,zippy2/libvirt,jardasgit/libvirt,taget/libvirt,jfehlig/libvirt,taget/libvirt,zippy2/libvirt,fabianfreyer/libvirt,VenkatDatta/libvirt,eskultety/libvirt,fabianfreyer/libvirt,VenkatDatta/libvirt,jfehlig/libvirt,crobinso/libvirt,olafhering/libvirt,eskultety/libvirt,datto/libvirt,fabianfreyer/libvirt,nertpinx/libvirt,fabianfreyer/libvirt,crobinso/libvirt,crobinso/libvirt,VenkatDatta/libvirt,crobinso/libvirt,eskultety/libvirt,eskultety/libvirt,andreabolognani/libvirt,taget/libvirt,zippy2/libvirt,VenkatDatta/libvirt,olafhering/libvirt,zippy2/libvirt,andreabolognani/libvirt,olafhering/libvirt,jardasgit/libvirt,VenkatDatta/libvirt,nertpinx/libvirt,jardasgit/libvirt,datto/libvirt,jardasgit/libvirt,libvirt/libvirt,andreabolognani/libvirt,datto/libvirt,libvirt/libvirt,jfehlig/libvirt,libvirt/libvirt,fabianfreyer/libvirt,taget/libvirt,nertpinx/libvirt,nertpinx/libvirt,andreabolognani/libvirt