util: Have virCommand remember whether limits are set
util: Have virCommand remember whether limits are set

Currently this only happens for the core size, but we want the
behavior to be consistent for other limits as well.

Signed-off-by: Andrea Bolognani <3ada0bee826c753786fdbba72243dfba997094cf@redhat.com>
Reviewed-by: Michal Privoznik <83d82aaba2eed257f4814b0c239c260c4caaadf0@redhat.com>

crobinso/libvirt,olafhering/libvirt,nertpinx/libvirt,libvirt/libvirt,zippy2/libvirt,nertpinx/libvirt,zippy2/libvirt,nertpinx/libvirt,nertpinx/libvirt,olafhering/libvirt,libvirt/libvirt,jfehlig/libvirt,libvirt/libvirt,crobinso/libvirt,crobinso/libvirt,zippy2/libvirt,olafhering/libvirt,zippy2/libvirt,crobinso/libvirt,nertpinx/libvirt,olafhering/libvirt,jfehlig/libvirt,jfehlig/libvirt,libvirt/libvirt,jfehlig/libvirt