Fix xmconfigtest
Fix xmconfigtest

Commit ac63014c introduced a regression in the conversion of Xen
xm config to XML by emitting an empty <cmdline>.  Prior to this
commit, <cmdline> was omitted if the xm config was missing (or
contained an empty) 'extra='.

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