Xen required a few changes in order to be usable:
* Include xenfs module in initrd as loading it in the activation
script was failing.
* Include /etc/default/xendomains, which is needed by
xen-domains service.
* Create /var/log/xen and /var/lib/xen directories in
the xen-store service, which are needed by the xl command.
The directories could be created by any other script as long as
they are guaranteed to exist before xl is called.
* Fix a reference to /bin/ls in the xendomains script.
Using pkgs.lib on the spine of module evaluation is problematic
because the pkgs argument depends on the result of module
evaluation. To prevent an infinite recursion, pkgs and some of the
modules are evaluated twice, which is inefficient. Using ‘with lib’
prevents this problem.
(systemd service descriptions that is, not service descriptions in "man
configuration.nix".)
Capitalizing each word in the description seems to be the accepted
standard.
Also shorten these descriptions:
* "Munin node, the agent process" => "Munin Node"
* "Planet Venus, an awesome ‘river of news’ feed reader" => "Planet Venus Feed Reader"
