virt-builder allows you to quickly create virtual machine images. It is part of libguestfs.

http://libguestfs.org/virt-builder.1.html

To create a virtual machine, run

virt-builder fedora-23 --root-password password:123456

This will create a virtual machine image with name fedora-23.img in current directory with password 123456.

Now you can create virtual machine based on this image with virt-install command.

 virt-install --import \
   --name f23vm1 --ram 2048 \
   --disk path=fedora-23.img,format=raw --os-variant fedora23