Fix handling of security driver restore failures in QEMU domain save

Fix handling of security driver restore failures in QEMU domain save

In cases where the security driver failed to restore a label after a
guest has saved, we mistakenly jumped to the error cleanup paths.
This is not good, because the operation has in fact completed and
cannot be rolled back completely. Label restore is non-critical, so
just log the problem instead. Also add a missing restore call in
the error cleanup path

* src/qemu/qemu_driver.c: Fix handling of security driver
  restore failures in QEMU domain save