qemuDomainCreateDeviceRecursive: Don't try to create devices under preserved mount points
    
    While the code allows devices to already be there (by some
    miracle), we shouldn't try to create devices that don't belong to
    us. For instance, we shouldn't try to create /dev/shm/file
    because /dev/shm is a mount point that is preserved. Therefore if
    a file is created there from an outside (e.g. by mgmt application
    or some other daemon running on the system like vhostmd), it
    exists in the qemu namespace too as the mount point is the same.
    It's only /dev and /dev only that is different. The same
    reasoning applies to all other preserved mount points.
    
    Signed-off-by: Michal Privoznik <mprivozn@redhat.com>
    Reviewed-by: Cedric Bosdonnat <cbosdonnat@suse.com>