iotests: Use $PYTHON for Python scripts

Instead of invoking Python scripts directly via ./, use $PYTHON to
obtain the correct Python interpreter command.

Signed-off-by: Max Reitz <mreitz@redhat.com>
Reviewed-by: Fam Zheng <famz@redhat.com>
Signed-off-by: Kevin Wolf <kwolf@redhat.com>
diff --git a/tests/qemu-iotests/036 b/tests/qemu-iotests/036
index 03b6aa9..a773653 100755
--- a/tests/qemu-iotests/036
+++ b/tests/qemu-iotests/036
@@ -53,15 +53,15 @@
 echo === Create image with unknown autoclear feature bit ===
 echo
 _make_test_img 64M
-./qcow2.py "$TEST_IMG" set-feature-bit autoclear 63
-./qcow2.py "$TEST_IMG" dump-header
+$PYTHON qcow2.py "$TEST_IMG" set-feature-bit autoclear 63
+$PYTHON qcow2.py "$TEST_IMG" dump-header
 
 echo
 echo === Repair image ===
 echo
 _check_test_img -r all
 
-./qcow2.py "$TEST_IMG" dump-header
+$PYTHON qcow2.py "$TEST_IMG" dump-header
 
 # success, all done
 echo "*** done"