virsh: improve help text for vol query commands
virsh: improve help text for vol query commands

Improves the help text for vol-path, vol-name, and vol-key, which
previously referred to volume UUIDs.

Addresses BZ # 598365.

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