test: Disable busy swap on scsi_debug

When e.g. TestStorageswap.test fails in the middle, the active swap
partition on the scsi_debug driver will prevent the module removal, and
break all subsequent tests.

Helps with #19683

Cherry-picked from 6c3986d

test/common/testlib.py

@@ -1540,6 +1540,7 @@ def cleanup_home_dirs():
                         "    done; "
                         "    while fuser --mount /dev/$dev --kill; do sleep 0.1; done; "
                         "    umount /dev/$dev || true; "
+                        "    swapon --show=NAME --noheadings | grep $dev | xargs -r swapoff; "
                         "done; until rmmod scsi_debug; do sleep 0.2; done", stdout=None)
 
         def terminate_sessions():