Instead of extracting a downloaded Gentoo filesystem tree into a file
containing a reiserfs filesystem, create an ext3 filesystem inside a
sparse file, mount it and debootstrap an up-to-date Debian system. Use
this image as base for all UML guest images.
Also, drop support for the various consoles and use xterm
unconditionally.
By using the ControlMaster and ControlPath options, existing SSH sessions
are reused (a session to each host is opened at the beginning of a test
run). Also, RC4 is used as encryption algorithm to further improve the
performance. These changes reduce the runtime by over 20%.