AUM: diskfull: rework the test

Test is reworked to be more reliable and prevent the system reboot.
Added `core.min-free-space-percent = 0` option to avoid complex
calculation and re-creation of big file.

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

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

@@ -28,28 +28,35 @@ run:
     - $ sudo ostree admin status
     - "Need to monitor the journal log"
     - $ sudo journalctl -ef --unit apertis-update-manager &
-    - "Check the free space on rootfs, calculate the size of file to leave only 3% of free space.
-      For instance,  NUM=2604620 for case below -- just round to lesser value the result of calculation: 2716616-(3733136/100*3)"
-    - $ sudo df -B 512 /
+    - "Check the free space on rootfs, calculate the size of file to leave insufficient free space for upgrade to happen
+      (this prevents the unexpected reboot during the test caused by other services).
+      For instance, in the case below, NUM value would be 1451. It is the result of the calculation 1823-348-24,
+      there 24 is a magic constant, so that almost, but not all free space is used.
+      The free space can be calculated with command line `sudo df -B 1M / | grep / | awk '{print $2-$3-24}'`"
+    - $ sudo df -B 1M /
     - | 
-        >Filesystem         512B-blocks      Used Available Use% Mounted on
-        /dev/mmcblk0p2         3733136    790784   2716616  23% /
-    - $ sudo dd if=/dev/zero of=/var/bigfile bs=512 count=<NUM>
-    - "Plug the USB flash drive in the device"
-    - "The update should fail with some error message related to disk space, for instance:"
+        >Filesystem           1M-blocks      Used Available Use% Mounted on
+        /dev/mmcblk0p2            1823       348      1365  21% /
+    - $ sudo dd if=/dev/zero of=/var/bigfile bs=1M count=<NUM> ; echo "dd completed!"
+    - Wait until 'dd' completes (it should take time),  you will see the output similar to
     - |
-        >Dec 19 22:55:10 apertis apertis-update-[319]: Ostree upgrade failed: mkdir(boot/loader.0/entries): Input/output error
-        Dec 19 22:43:46 apertis apertis-update-[794]: Ostree upgrade failed: Error writing to file descriptor: No space left on device
-    - "Remove the USB flash drive"
-    - "Remove temporary file"
-    - $ sudo rm -f /var/bigfile
-    - "Fill the disk with root filesystem to 100%"
-    - $ sudo dd if=/dev/zero of=/var/bigfile bs=1M
+        >1521483776 bytes (1.5 GB) copied, 82.1661 s, 18.5 MB/s
+        dd completed!
     - "Plug the USB flash drive in the device"
     - "The update should fail with error message"
     - |
         >Dec 19 22:53:33 apertis apertis-update-[348]: Ostree upgrade failed: min-free-space-percent '3%' would be exceeded, 16.8 MB available
     - "Remove the USB flash drive"
+    - Set reserved space for ostree to '0'
+    - $ sudo ostree config set core.min-free-space-percent "0"
+    - Restart the Apertis Update Manager
+    - $ sudo systemctl restart apertis-update-manager
+    - "Plug the USB flash drive in the device"
+    - "The update should fail with some error message related to disk space, for instance:"
+    - |
+        >Dec 19 22:55:10 apertis apertis-update-[319]: Ostree upgrade failed: mkdir(boot/loader.0/entries): Input/output error
+        Dec 19 22:43:46 apertis apertis-update-[794]: Ostree upgrade failed: Error writing to file descriptor: No space left on device
+    - "Remove the USB flash drive"
     - "Remove temporary file"
     - $ sudo rm -f /var/bigfile
     - "Reboot the system"