xen: Make xenDaemon*DeviceFlags errors less confusing
xen: Make xenDaemon*DeviceFlags errors less confusing

When a user calls to virDomain{Attach,Detach,Update}DeviceFlags() with
flags == VIR_DOMAIN_DEVICE_MODIFY_LIVE on an inactive guest running on
an old Xen hypervisor (such as RHEL-5) xend_internal driver reports:

    Xend version does not support modifying persistent config

which is pretty confusing since no-one requested to modify persistent
config.

foomango/libvirt,datto/libvirt,amery/libvirt-vserver,elmarco/libvirt,andreabolognani/libvirt,cbosdo/libvirt,amery/libvirt-vserver,libvirt/libvirt,datto/libvirt,emaste/libvirt,danwent/libvirt-ovs,libvirt/libvirt,fabianfreyer/libvirt,foomango/libvirt,agx/libvirt,libvirt/libvirt,kantai/libvirt-vfork,olafhering/libvirt,zippy2/libvirt,rmarwaha/libvirt1,jfehlig/libvirt,eskultety/libvirt,nertpinx/libvirt,elmarco/libvirt,soulxu/libvirt-xuhj,foomango/libvirt,fabianfreyer/libvirt,trainstack/libvirt,sshah-solarflare/Libvirt-PCI-passthrough-,usc-isi/libvirt,taget/libvirt,novel/fbsd-libvirt,crobinso/libvirt,sshah-solarflare/Libvirt-PCI-passthrough-,warewolf/libvirt,trainstack/libvirt,novel/fbsd-libvirt,iam-TJ/libvirt,rbu/libvirt,usc-isi/libvirt,rmarwaha/libvirt1,olafhering/libvirt,zippy2/libvirt,agx/libvirt,rmarwaha/libvirt1,leilihh/libvirt,libvirt/libvirt,amery/libvirt-vserver,sshah-solarflare/Libvirt-PCI-passthrough-,rlaager/libvirt,fabianfreyer/libvirt,jardasgit/libvirt,jfehlig/libvirt,zippy2/libvirt,warewolf/libvirt,kantai/libvirt-vfork,elmarco/libvirt,emaste/libvirt,rbu/libvirt,novel/fbsd-libvirt,fabianfreyer/libvirt,andreabolognani/libvirt,shugaoye/libvirt,shugaoye/libvirt,cbosdo/libvirt,VenkatDatta/libvirt,novel/fbsd-libvirt,nertpinx/libvirt,trainstack/libvirt,datto/libvirt,siboulet/libvirt-openvz,wiedi/libvirt,crobinso/libvirt,agx/libvirt,zhlcindy/libvirt-1.1.4-maintain,rbu/libvirt,siboulet/libvirt-openvz,zhlcindy/libvirt-1.1.4-maintain,shugaoye/libvirt,zhlcindy/libvirt-1.1.4-maintain,rmarwaha/libvirt,jeckersb/libvirt,VenkatDatta/libvirt,rlaager/libvirt,wiedi/libvirt,kantai/libvirt-vfork,kantai/libvirt-vfork,wiedi/libvirt,amery/libvirt-vserver,jeckersb/libvirt,emaste/libvirt,rmarwaha/libvirt,soulxu/libvirt-xuhj,iam-TJ/libvirt,jeckersb/libvirt,iam-TJ/libvirt,jfehlig/libvirt,nertpinx/libvirt,soulxu/libvirt-xuhj,bjzhang/libvirt,rlaager/libvirt,soulxu/libvirt-xuhj,wiedi/libvirt,wiedi/libvirt,rmarwaha/libvirt,warewolf/libvirt,crobinso/libvirt,rbu/libvirt,zippy2/libvirt,cbosdo/libvirt,leilihh/libvirt,bjzhang/libvirt,leilihh/libvirt,dumbbell/libvirt,rbu/libvirt,VenkatDatta/libvirt,warewolf/libvirt,crobinso/libvirt,elmarco/libvirt,trainstack/libvirt,bjzhang/libvirt,jeckersb/libvirt,trainstack/libvirt,siboulet/libvirt-openvz,rmarwaha/libvirt,cbosdo/libvirt,jardasgit/libvirt,dumbbell/libvirt,datto/libvirt,eskultety/libvirt,eskultety/libvirt,rmarwaha/libvirt,novel/fbsd-libvirt,jardasgit/libvirt,danwent/libvirt-ovs,eskultety/libvirt,leilihh/libvirt,taget/libvirt,bjzhang/libvirt,olafhering/libvirt,novel/fbsd-libvirt,dumbbell/libvirt,bjzhang/libvirt,cbosdo/libvirt,foomango/libvirt,emaste/libvirt,iam-TJ/libvirt,warewolf/libvirt,shugaoye/libvirt,danwent/libvirt-ovs,iam-TJ/libvirt,kantai/libvirt-vfork,emaste/libvirt,foomango/libvirt,rlaager/libvirt,taget/libvirt,zhlcindy/libvirt-1.1.4-maintain,datto/libvirt,VenkatDatta/libvirt,jardasgit/libvirt,nertpinx/libvirt,warewolf/libvirt,eskultety/libvirt,emaste/libvirt,rmarwaha/libvirt1,zhlcindy/libvirt-1.1.4-maintain,novel/fbsd-libvirt,usc-isi/libvirt,taget/libvirt,iam-TJ/libvirt,siboulet/libvirt-openvz,agx/libvirt,leilihh/libvirt,andreabolognani/libvirt,rlaager/libvirt,fabianfreyer/libvirt,dumbbell/libvirt,danwent/libvirt-ovs,andreabolognani/libvirt,nertpinx/libvirt,elmarco/libvirt,wiedi/libvirt,VenkatDatta/libvirt,jeckersb/libvirt,jeckersb/libvirt,siboulet/libvirt-openvz,rmarwaha/libvirt1,agx/libvirt,amery/libvirt-vserver,jardasgit/libvirt,danwent/libvirt-ovs,dumbbell/libvirt,dumbbell/libvirt,warewolf/libvirt,rmarwaha/libvirt1,rmarwaha/libvirt,usc-isi/libvirt,emaste/libvirt,andreabolognani/libvirt,taget/libvirt,sshah-solarflare/Libvirt-PCI-passthrough-,novel/fbsd-libvirt,shugaoye/libvirt,novel/fbsd-libvirt,sshah-solarflare/Libvirt-PCI-passthrough-,jeckersb/libvirt,iam-TJ/libvirt,jfehlig/libvirt,wiedi/libvirt,leilihh/libvirt,olafhering/libvirt,usc-isi/libvirt,trainstack/libvirt,trainstack/libvirt,soulxu/libvirt-xuhj