Rewrite qemu-img backing store format handling
Rewrite qemu-img backing store format handling

When creating qcow2 files with a backing store, it is important
to set an explicit format to prevent QEMU probing. The storage
backend was only doing this if it found a 'kvm-img' binary. This
is wrong because plenty of kvm-img binaries don't support an
explicit format, and plenty of 'qemu-img' binaries do support
a format. The result was that most qcow2 files were not getting
a backing store format.

This patch runs 'qemu-img -h' to check for the two support
argument formats

  '-o backing_format=raw'
  '-F raw'

and use whichever option it finds

* src/storage/storage_backend.c: Query binary to determine
  how to set the backing store format

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