node_memory: Fix bug of node_memory_tune
node_memory: Fix bug of node_memory_tune

The 3 options accept 0, and merely checking for non-zero values
would cause wrong results.

cbosdo/libvirt,trainstack/libvirt,jardasgit/libvirt,elmarco/libvirt,elmarco/libvirt,iam-TJ/libvirt,elmarco/libvirt,VenkatDatta/libvirt,bjzhang/libvirt,libvirt/libvirt,jeckersb/libvirt,nertpinx/libvirt,crobinso/libvirt,fabianfreyer/libvirt,bjzhang/libvirt,jfehlig/libvirt,shugaoye/libvirt,jeckersb/libvirt,VenkatDatta/libvirt,zhlcindy/libvirt-1.1.4-maintain,eskultety/libvirt,datto/libvirt,elmarco/libvirt,libvirt/libvirt,libvirt/libvirt,iam-TJ/libvirt,andreabolognani/libvirt,rlaager/libvirt,siboulet/libvirt-openvz,rlaager/libvirt,zippy2/libvirt,crobinso/libvirt,siboulet/libvirt-openvz,jeckersb/libvirt,iam-TJ/libvirt,trainstack/libvirt,zippy2/libvirt,zhlcindy/libvirt-1.1.4-maintain,cbosdo/libvirt,fabianfreyer/libvirt,crobinso/libvirt,crobinso/libvirt,zhlcindy/libvirt-1.1.4-maintain,agx/libvirt,taget/libvirt,jardasgit/libvirt,taget/libvirt,fabianfreyer/libvirt,zhlcindy/libvirt-1.1.4-maintain,elmarco/libvirt,siboulet/libvirt-openvz,datto/libvirt,jeckersb/libvirt,nertpinx/libvirt,iam-TJ/libvirt,shugaoye/libvirt,siboulet/libvirt-openvz,jeckersb/libvirt,eskultety/libvirt,iam-TJ/libvirt,olafhering/libvirt,siboulet/libvirt-openvz,jeckersb/libvirt,cbosdo/libvirt,nertpinx/libvirt,andreabolognani/libvirt,taget/libvirt,datto/libvirt,jardasgit/libvirt,iam-TJ/libvirt,jardasgit/libvirt,fabianfreyer/libvirt,libvirt/libvirt,emaste/libvirt,olafhering/libvirt,VenkatDatta/libvirt,trainstack/libvirt,emaste/libvirt,andreabolognani/libvirt,VenkatDatta/libvirt,nertpinx/libvirt,cbosdo/libvirt,iam-TJ/libvirt,zhlcindy/libvirt-1.1.4-maintain,taget/libvirt,jfehlig/libvirt,bjzhang/libvirt,emaste/libvirt,rlaager/libvirt,VenkatDatta/libvirt,bjzhang/libvirt,shugaoye/libvirt,eskultety/libvirt,zippy2/libvirt,trainstack/libvirt,shugaoye/libvirt,jeckersb/libvirt,jardasgit/libvirt,emaste/libvirt,trainstack/libvirt,andreabolognani/libvirt,agx/libvirt,emaste/libvirt,emaste/libvirt,agx/libvirt,andreabolognani/libvirt,eskultety/libvirt,agx/libvirt,rlaager/libvirt,cbosdo/libvirt,eskultety/libvirt,trainstack/libvirt,emaste/libvirt,trainstack/libvirt,nertpinx/libvirt,taget/libvirt,agx/libvirt,datto/libvirt,jfehlig/libvirt,datto/libvirt,rlaager/libvirt,bjzhang/libvirt,olafhering/libvirt,shugaoye/libvirt,olafhering/libvirt,jfehlig/libvirt,fabianfreyer/libvirt,zippy2/libvirt