Fix autostart flag when loading running domains

Fix autostart flag when loading running domains

Drivers load running persistent and transient domain configs before
inactive persistent domain configs, however only the latter would set a
domain's autostart flag. This mismatch between the loaded and on-disk
state could later cause problems with "virsh autostart":

  # virsh autostart example
  error: Failed to mark domain example as autostarted
  error: Failed to create symlink '/etc/libvirt/qemu/autostart/example.xml to '/etc/libvirt/qemu/example.xml': File exists

This patch ensures the autostart flag is set correctly even when the
domain is already defined.

Fixes:

  https://bugzilla.redhat.com/show_bug.cgi?id=632100
  https://bugzilla.redhat.com/show_bug.cgi?id=675319

Signed-off-by: Michael Chapman <mike@very.puzzling.org>