[archiso] Update fstab and "source dev" of aufs.

* Change from none -> union (looks like util-linux is confused BUG?)
    Avoid the message: "umount aufs failed: not found" at shutdown.
    #1 mount -t tmpfs none /something
    #2 mount -t tmpfs xxxx /something
    The output of findmnt -rnu -o SOURCE will be blank in #1

.

* Change from aufs -> auto, make its more generic.

* Update devpts and shm entries.
Signed-off-by: Gerardo Exequiel Pozzi <vmlinuz386@yahoo.com.ar>

archiso/hooks/archiso

@@ -127,7 +127,7 @@ archiso_mount_handler() {
     msg "done."
 
     msg ":: Mounting root (aufs) filesystem"
-    /bin/mount -t aufs -o dirs=/rw_branch=rw none "${newroot}"
+    /bin/mount -t aufs -o dirs=/rw_branch=rw union "${newroot}"
     if [ $? -ne 0 ]; then
         echo "ERROR: while mounting root (aufs) filesystem."
         launch_interactive_shell

configs/syslinux-iso/overlay/etc/fstab

+#
 # /etc/fstab: static file system information
+#
 # <file system>        <dir>         <type>    <options>          <dump> <pass>
-aufs                   /             aufs      noauto              0      0
-none                   /dev/pts      devpts    defaults            0      0
-none                   /dev/shm      tmpfs     defaults            0      0
-
-### Auto generated entries get added here:
+union                  /             auto      noauto              0      0
+devpts                 /dev/pts      devpts    defaults            0      0
+shm                    /dev/shm      tmpfs     nodev,nosuid        0      0