snapshot: fix regression with system checkpoints
snapshot: fix regression with system checkpoints

Regression introduced in commit d6f6b2d194c.  Running
'virsh snapshot-create dom' would mistakenly report that
disks can only be specified for disk snapshots.

* src/conf/domain_conf.c (virDomainSnapshotDefParseString): Only
give error about no disk support when <disk> was found.

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