iotests: use qemu_img() in has_working_luks()

Admittedly a mostly lateral move, but qemu_img() is essentially the
replacement for qemu_img_pipe_and_status(). It will give slightly better
diagnostics on crash.

Signed-off-by: John Snow <jsnow@redhat.com>
Reviewed-by: Hanna Reitz <hreitz@redhat.com>
Message-Id: <20220321201618.903471-16-jsnow@redhat.com>
Signed-off-by: Hanna Reitz <hreitz@redhat.com>

tests/qemu-iotests/iotests.py

@@ -1445,20 +1445,20 @@ def has_working_luks() -> Tuple[bool, str]:
     """
 
     img_file = f'{test_dir}/luks-test.luks'
-    (output, status) = \
-        qemu_img_pipe_and_status('create', '-f', 'luks',
-                                 '--object', luks_default_secret_object,
-                                 '-o', luks_default_key_secret_opt,
-                                 '-o', 'iter-time=10',
-                                 img_file, '1G')
+    res = qemu_img('create', '-f', 'luks',
+                   '--object', luks_default_secret_object,
+                   '-o', luks_default_key_secret_opt,
+                   '-o', 'iter-time=10',
+                   img_file, '1G',
+                   check=False)
     try:
         os.remove(img_file)
     except OSError:
         pass
 
-    if status != 0:
-        reason = output
-        for line in output.splitlines():
+    if res.returncode:
+        reason = res.stdout
+        for line in res.stdout.splitlines():
             if img_file + ':' in line:
                 reason = line.split(img_file + ':', 1)[1].strip()
                 break