Downspeed the read from USB flash during AUM USB unplug test

Need to reduce the read speed for the test since recent libostree do not
read the whole update bundle during the test.

Signed-off-by: Denis Pynkin <denis.pynkin@collabora.com>

test-cases/apertis-update-manager-usb-unplug.yaml

@@ -43,10 +43,10 @@ run:
     - "The booted commit (started with '*') must have ID which we prepare and the initial commit ID should be marked as '(rollback)'"
     - "Remove the initial deployment"
     - $ sudo ostree admin undeploy 1
-    - "Add udev rule for limiting the maximal read speed from USB drive to 1MBps."
+    - "Add udev rule for limiting the maximal read speed from USB drive to 64Kbps."
     - $ sudo tee /etc/udev/rules.d/99-usblimit.rules <<"EOF"
     - |
-        >KERNEL=="sd*", SUBSYSTEMS=="usb", ACTION=="add", ENV{DEVTYPE}=="disk", ENV{MAJOR}=="8", RUN+="/bin/sh -c 'echo $env{MAJOR}:$env{MINOR} 1048576 > /sys/fs/cgroup/blkio/blkio.throttle.read_bps_device'"
+        >KERNEL=="sd*", SUBSYSTEMS=="usb", ACTION=="add", ENV{DEVTYPE}=="disk", ENV{MAJOR}=="8", RUN+="/bin/sh -c 'echo $env{MAJOR}:$env{MINOR} 65536 > /sys/fs/cgroup/blkio/blkio.throttle.read_bps_device'"
         EOF
     - "Reboot the system"
     - "Check the current deployment"
@@ -55,11 +55,12 @@ run:
     - $ sudo journalctl -ef --unit apertis-update-manager &
     - "Plug the USB flash drive into the device"
     - "The update starts automatically"
-    - "Wait while the upgrade starts (5-20 seconds depending on your HW) and remove the USB flash drive before it is completed:"
+    - "Wait while the upgrade starts:"
     - |
         >Dec 19 22:31:46 apertis apertis-update-[390]: mount added : /media/test
         Dec 19 22:31:46 apertis apertis-update-[390]: Ostree static delta starting
         Dec 19 22:31:46 apertis apertis-update-[390]: Cannot check the ID in black list: No such file or directory
+    - "Wait for 5-20 seconds (depending on your HW) and remove the USB flash drive before it is completed."
     - "Update should be interrupted with error messages similar to"
     - |
         >[   59.542717] scsi 1:0:0:0: rejecting I/O to offline device