iotests: use qemu_img_json() when applicable

qemu_img_json() gives better diagnostic information on failure.

Signed-off-by: John Snow <jsnow@redhat.com>
Reviewed-by: Hanna Reitz <hreitz@redhat.com>
Message-Id: <20220321201618.903471-8-jsnow@redhat.com>
Signed-off-by: Hanna Reitz <hreitz@redhat.com>

tests/qemu-iotests/iotests.py

@@ -309,11 +309,11 @@ def qemu_img_json(*args: str) -> Any:
 
     return json.loads(res.stdout)
 
-def qemu_img_measure(*args):
-    return json.loads(qemu_img_pipe("measure", "--output", "json", *args))
+def qemu_img_measure(*args: str) -> Any:
+    return qemu_img_json("measure", "--output", "json", *args)
 
-def qemu_img_check(*args):
-    return json.loads(qemu_img_pipe("check", "--output", "json", *args))
+def qemu_img_check(*args: str) -> Any:
+    return qemu_img_json("check", "--output", "json", *args)
 
 def qemu_img_pipe(*args: str) -> str:
     '''Run qemu-img and return its output'''