Refactor the libvirt RPM daemon pieces

There are a number of flaws with our packaging of the libvirtd
daemon:

 - Installing 'libvirt' does not install 'qemu-kvm' or 'xen'
   etc which are required to actually run the hypervisor in
   question
 - Installing 'libvirt' pulls in the default configuration
   files which may not be wanted & cause problems if installed
   inside a guest
 - It is not possible to explicitly required all the peices
   required to manage a specific hypervisor

This change takes the 'libvirt' RPM and and changes it thus

 - libvirt: just a virtual package with dep on libvirt-daemon,
   libvirt-daemon-config-network & libvirt-daemon-config-nwfilter
 - libvirt-daemon: the libvirt daemon and related pieces
 - libvirt-daemon-config-network: the default network config
 - libvirt-daemon-config-nwfilter: the network filter configs
 - libvirt-docs: the website HTML

We then introduce some more virtual (empty) packages

 - libvirt-daemon-qemu: Deps on libvirt-daemon & 'qemu'
 - libvirt-daemon-kvm: Deps on libvirt-daemon & 'qemu-kvm'
 - libvirt-daemon-lxc: Deps on libvirt-daemon
 - libvirt-daemon-uml: Deps on libvirt-daemon
 - libvirt-daemon-xen: Deps on libvirt-daemon & 'xen'

 - libvirt-qemu: Deps on libvirt-daemon-qemu & libvirt-daemon-config-{network,nwfilter}
 - libvirt-kvm: Deps on libvirt-daemon-kvm & libvirt-daemon-config-{network,nwfilter}
 - libvirt-lxc: Deps on libvirt-daemon-lxc & libvirt-daemon-config-{network,nwfilter}
 - libvirt-uml: Deps on libvirt-daemon-uml & libvirt-daemon-config-{network,nwfilter}
 - libvirt-xen: Deps on libvirt-daemon-xen & libvirt-daemon-config-network

My intent in the future is to turn on the driver modules by
default, at which time 'libvirt-daemon' will cease to include
any specific drivers, instead we'll get libvirt-daemon-driver-XXXX
packages for each driver. The libvirt-daemon-XXX packages will
then pull in each driver that they require.

It is recommended that applications required a locally installed
libvirtd daemon, use either 'Requires: libvirt-daemon-XXXX' or
'Requires: libvirt-XXX' and *not* "Requires: libvirt-daemon"
or 'Requires: libvirt'

* libvirt.spec.in: Refactor RPMs
* docs/packaging.html.in, docs/sitemap.html.in: Document
  new RPM split rationale

docs/sitemap.html.in

@@ -84,6 +84,10 @@
                 <a href="hooks.html">Hooks</a>
                 <span>Hooks for system specific management</span>
               </li>
+              <li>
+                <a href="packaging.html">Distribution packaging</a>
+                <span>Rationale for distribution RPM packaging</span>
+              </li>
             </ul>
           </li>
           <li>