Update example layouts

Addresses the problem that the example layout files contains services
and properties that no longer exist or have been deprecated.

Addresses the problem that the head.conf example layout file is a
rather bad example of how to place services in domains. Too many sites
have copied this layout, believing it is a good setup for a head node.
The problem is addressed by removing this layout.

Addresses the problem that our default layout is single, even though
best practice recommendation is to use the host name. The default is
now the host name. This affects sites on upgrade if they relied on the
old default.

Addresses the problem that we ship example files in a configuration
directory. Instead these are now placed in /usr/share/dcache/examples/layouts.

Release notes should probably contain a note reminding RPM users that if
they called their layout file either single, head or pool, that they
should check that RPM didn't rename their layout file.

Target: trunk
Request: 2.7
Require-notes: yes
Require-book: yes
Acked-by: Paul Millar <paul.millar@desy.de>
Patch: http://rb.dcache.org/r/6076/