When running in libvirtd, we are happy for any of the drivers to simply
skip their initialization in virStateInitialize, as other drivers are
still potentially useful.

When running in per-driver daemons though, we want the daemon to abort
startup if the driver cannot initialize itself, as the daemon will be
useless without it.
Reviewed-by: NAndrea Bolognani <abologna@redhat.com>
Signed-off-by: NDaniel P. Berrangé <berrange@redhat.com>