Add a domain argument to SVirt *RestoreImageLabel

Add a domain argument to SVirt *RestoreImageLabel

When James Morris originally submitted his sVirt patches (as seen in
libvirt 0.6.1), he did not require on disk labelling for
virSecurityDomainRestoreImageLabel. A later commit[2] changed this
behavior to assume on disk labelling, which halts implementations for
path-based MAC systems such as AppArmor and TOMOYO where
vm->def->seclabel is required to obtain the label.

* src/security/security_driver.h src/qemu/qemu_driver.c
  src/security/security_selinux.c: adds the 'virDomainObjPtr vm'
  argument back to *RestoreImageLabel