Some architectures in certain RHEL versions do not include any
hypervisors. Update the specfile to allow those to easily build
a remote client only version of libvirt. ie no libvirtd related
bits at all.

* qemud/Makefile.am: Always instal SASL config since its needed
  by client too
* libvirt.spec.in: Re-factor specfile conditionals to allow entire
  server side build to be disabled easily, eg a remote client only
  build. Make RHEL-5 do client only build for s390/ppc. Make RHEL-6
  do a client only build for all non-x86_64 archs. Enable LXC on
  RHEL-6. Enable all Fedora >= 6 features on RHEL-6 too. Add some
  more conditionals around dnsmasq/iptables/hal Requires tags.
  Add missing e2fsprogs-devel BR for RHEL-5 as workaround for broken
  parted. Fix the device mapper BR for RHEL-5. Add conditional rules
  for ESX build. Add conditional rules for SELinux + HAL builds.
  Fix a mistaken %{with_qemu} to be %{with_network} when setting
  up default network XML