qemu: keep pre-migration domain state after failed migration
    
    Couple of codepaths shared the same code which can be moved out to a
    function and on one of such places, qemuMigrationConfirmPhase(), the
    domain was resumed even if it wasn't running before the migration
    started.
    
    Resolves: https://bugzilla.redhat.com/show_bug.cgi?id=1057407
    
    Signed-off-by: Martin Kletzander <mkletzan@redhat.com>