virsh: Update virsh man page
virsh: Update virsh man page

Valid loglevel range for virsh  is 0-4. Update virsh man page
accordingly. Also explain virsh ENV variables and values.

Signed-off-by: Supriya Kannery <c6dca644ab1b8497a0f872c2b7a4b4b4eef5a5f1@in.ibm.com>

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