tests: ensure that image validation will not cure the corruption

Since
    commit cfce1091
    Author: Alexander Ivanov <alexander.ivanov@virtuozzo.com>
    Date:   Tue Jul 18 12:44:29 2023 +0200
    parallels: Image repairing in parallels_open()
there is a potential pit fall with calling
    qemu-io -c "read"
The image is opened in read-write mode and thus could be potentially
repaired. This could ruin testing process.

The patch forces read-only opening for reads. In that case repairing
is impossible.

Signed-off-by: Denis V. Lunev <den@openvz.org>
Reviewed-by: Alexander Ivanov <alexander.ivanov@virtuozzo.com>

tests/qemu-iotests/tests/parallels-checks

@@ -91,7 +91,7 @@ file_size=`stat --printf="%s" "$TEST_IMG"`
 echo "file size: $file_size"
 
 echo "== check last cluster =="
-{ $QEMU_IO -c "read -P 0x11 $LAST_CLUSTER_OFF $CLUSTER_SIZE" "$TEST_IMG"; } 2>&1 | _filter_qemu_io | _filter_testdir
+{ $QEMU_IO -r -c "read -P 0x11 $LAST_CLUSTER_OFF $CLUSTER_SIZE" "$TEST_IMG"; } 2>&1 | _filter_qemu_io | _filter_testdir
 
 # Clear image
 _make_test_img $SIZE
@@ -105,19 +105,20 @@ echo "== write another pattern to second cluster =="
 { $QEMU_IO -c "write -P 0x55 $CLUSTER_SIZE $CLUSTER_SIZE" "$TEST_IMG"; } 2>&1 | _filter_qemu_io | _filter_testdir
 
 echo "== check second cluster =="
-{ $QEMU_IO -c "read -P 0x55 $CLUSTER_SIZE $CLUSTER_SIZE" "$TEST_IMG"; } 2>&1 | _filter_qemu_io | _filter_testdir
+{ $QEMU_IO -r -c "read -P 0x55 $CLUSTER_SIZE $CLUSTER_SIZE" "$TEST_IMG"; } 2>&1 | _filter_qemu_io | _filter_testdir
+
 
 echo "== corrupt image =="
 poke_file "$TEST_IMG" "$(($BAT_OFFSET + 4))" "\x01\x00\x00\x00"
 
 echo "== check second cluster =="
-{ $QEMU_IO -c "read -P 0x11 $CLUSTER_SIZE $CLUSTER_SIZE" "$TEST_IMG"; } 2>&1 | _filter_qemu_io | _filter_testdir
+{ $QEMU_IO -r -c "read -P 0x11 $CLUSTER_SIZE $CLUSTER_SIZE" "$TEST_IMG"; } 2>&1 | _filter_qemu_io | _filter_testdir
 
 echo "== repair image =="
 _check_test_img -r all
 
 echo "== check second cluster =="
-{ $QEMU_IO -c "read -P 0x11 $CLUSTER_SIZE $CLUSTER_SIZE" "$TEST_IMG"; } 2>&1 | _filter_qemu_io | _filter_testdir
+{ $QEMU_IO -r -c "read -P 0x11 $CLUSTER_SIZE $CLUSTER_SIZE" "$TEST_IMG"; } 2>&1 | _filter_qemu_io | _filter_testdir
 
 echo "== check first cluster on host =="
 printf "content: 0x%02x\n" `peek_file_le $TEST_IMG $(($CLUSTER_SIZE)) 1`