iotests: add script_initialize

Like script_main, but doesn't require a single point of entry.
Replace all existing initialization sections with this drop-in replacement.

This brings debug support to all existing script-style iotests.

Signed-off-by: John Snow <jsnow@redhat.com>
Reviewed-by: Max Reitz <mreitz@redhat.com>
Message-Id: <20200331000014.11581-12-jsnow@redhat.com>
Reviewed-by: Kevin Wolf <kwolf@redhat.com>
[mreitz: Give 274 the same treatment]
Signed-off-by: Max Reitz <mreitz@redhat.com>
diff --git a/tests/qemu-iotests/248 b/tests/qemu-iotests/248
index 68c3746..18ba034 100755
--- a/tests/qemu-iotests/248
+++ b/tests/qemu-iotests/248
@@ -21,7 +21,7 @@
 import iotests
 from iotests import qemu_img_create, qemu_io, file_path, filter_qmp_testfiles
 
-iotests.verify_image_format(supported_fmts=['qcow2'])
+iotests.script_initialize(supported_fmts=['qcow2'])
 
 source, target = file_path('source', 'target')
 size = 5 * 1024 * 1024