Limit I/O read speed for AUM powercut test

Use CGroups blkio to limit the read speed to 1MBps allowing to
remove the USB flash in predictable state even on extremely fast
devices.

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

test-cases/apertis-update-manager-powercut.yaml

@@ -45,6 +45,11 @@ 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."
+    - $ 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'"
+        EOF
     - "Reboot the system"
     - "Check the current deployment"
     - $ sudo ostree admin status