appliance: Quiet some warnings about missing files.

Try to make the appliance script as quiet as possible along
the fast path.

appliance/init

@@ -81,9 +81,11 @@ fi
 
 # Disk optimizations.
 # Increase the SCSI timeout so we can read remote images.
+shopt -s nullglob
 for f in /sys/block/sd*/device/timeout; do echo 300 > $f; done
 # https://access.redhat.com/site/solutions/5427
 for f in /sys/block/{h,s,ub,v}d*/queue/scheduler; do echo noop > $f; done
+shopt -u nullglob
 
 # Update the system clock.
 hwclock -u -s