iotest 258: use script_main

Since this one is nicely factored to use a single entry point,
use script_main to run the tests.

Signed-off-by: John Snow <jsnow@redhat.com>
Reviewed-by: Philippe Mathieu-Daudé <philmd@redhat.com>
Reviewed-by: Max Reitz <mreitz@redhat.com>
Message-Id: <20200331000014.11581-13-jsnow@redhat.com>
Reviewed-by: Kevin Wolf <kwolf@redhat.com>
Signed-off-by: Max Reitz <mreitz@redhat.com>

tests/qemu-iotests/258

@@ -23,12 +23,6 @@ import iotests
 from iotests import log, qemu_img, qemu_io_silent, \
         filter_qmp_testfiles, filter_qmp_imgfmt
 
-# Need backing file and change-backing-file support
-iotests.script_initialize(
-    supported_fmts=['qcow2', 'qed'],
-    supported_platforms=['linux'],
-)
-
 # Returns a node for blockdev-add
 def node(node_name, path, backing=None, fmt=None, throttle=None):
     if fmt is None:
@@ -161,4 +155,7 @@ def main():
     test_concurrent_finish(False)
 
 if __name__ == '__main__':
-    main()
+    # Need backing file and change-backing-file support
+    iotests.script_main(main,
+                        supported_fmts=['qcow2', 'qed'],
+                        supported_platforms=['linux'])