Add a new 'access_drivers' config parameter to the libvirtd.conf
configuration file. This allows admins to setup the default
access control drivers to use for API authorization. The same
driver is to be used by all internal drivers & APIs
Signed-off-by: NDaniel P. Berrange <berrange@redhat.com>

When adding new config file parameters, the corresponding
additions to the augeas lens' are constantly forgotten.
Also there are augeas test cases, these don't catch the
error, since they too are never updated.

To address this, the augeas test cases need to be auto-generated
from the example config files.

* build-aux/augeas-gentest.pl: Helper to generate an
  augeas test file, substituting in elements from the
  example config files
* src/Makefile.am, daemon/Makefile.am: Switch to
  auto-generated augeas test cases
* daemon/test_libvirtd.aug, daemon/test_libvirtd.aug.in,
  src/locking/test_libvirt_sanlock.aug,
  src/locking/test_libvirt_sanlock.aug.in,
  src/lxc/test_libvirtd_lxc.aug,
  src/lxc/test_libvirtd_lxc.aug.in,
  src/qemu/test_libvirtd_qemu.aug,
  src/qemu/test_libvirtd_qemu.aug.in: Remove example
  config file data, replacing with a ::CONFIG:: placeholder
Signed-off-by: NDaniel P. Berrange <berrange@redhat.com>