block_with_write_threshold: Support luks format

The filename is json format if the image format is luks, so
need to parse them and to get block device node name by filename
item instead of file item.
Signed-off-by: NYongxue Hong <yhong@redhat.com>

qemu/tests/block_with_write_threshold.py

@@ -5,10 +5,10 @@ from avocado.utils.wait import wait_for
 
 from virttest import data_dir
 from virttest import error_context
-from virttest import storage
 from virttest import utils_disk
 from virttest import utils_test
 from virttest import utils_misc
+from virttest.qemu_storage import QemuImg, get_image_json
 
 from provider.storage_benchmark import generate_instance
 
@@ -36,10 +36,12 @@ def run(test, params, env):
     def get_node_name(image_tag):
         """ Get the node name. """
         img_params = params.object_params(image_tag)
-        file = storage.get_image_filename(img_params, data_dir.get_data_dir())
-        for block in vm.monitor.info("block"):
-            if file == block['inserted']['file']:
-                return block['inserted']['node-name']
+        root_dir = data_dir.get_data_dir()
+        img = QemuImg(img_params, root_dir, image_tag)
+        filename = img.image_filename
+        if img.image_format == 'luks':
+            filename = get_image_json(image_tag, img_params, root_dir)
+        return vm.get_block({"filename": filename})
 
     def set_block_write_threshold(monitor, node_name, size):
         """ Set block write threshold for the block drive. """