iotests: Fix up python style in 300

Break some long lines, and relax our type hints to be more generic to
any JSON, in order to more easily permit the additional JSON depth now
possible in migration parameters.  Detected by iotest 297.

Fixes: ca4bfec4
 (qemu-iotests: 300: Add test case for modifying persistence of bitmap)
Reported-by: Kevin Wolf <kwolf@redhat.com>
Signed-off-by: Eric Blake <eblake@redhat.com>
Message-Id: <20210215220518.1745469-1-eblake@redhat.com>
Reviewed-by: John Snow <jsnow@redhat.com>
Reviewed-by: Vladimir Sementsov-Ogievskiy <vsementsov@virtuozzo.com>
Signed-off-by: Kevin Wolf <kwolf@redhat.com>

tests/qemu-iotests/300

@@ -22,7 +22,7 @@
 import os
 import random
 import re
-from typing import Dict, List, Optional, Union
+from typing import Dict, List, Optional
 
 import iotests
 
@@ -30,7 +30,7 @@ import iotests
 # pylint: disable=wrong-import-order
 import qemu
 
-BlockBitmapMapping = List[Dict[str, Union[str, List[Dict[str, str]]]]]
+BlockBitmapMapping = List[Dict[str, object]]
 
 mig_sock = os.path.join(iotests.sock_dir, 'mig_sock')
 
@@ -602,7 +602,8 @@ class TestCrossAliasMigration(TestDirtyBitmapMigration):
 
 class TestAliasTransformMigration(TestDirtyBitmapMigration):
     """
-    Tests the 'transform' option which modifies bitmap persistence on migration.
+    Tests the 'transform' option which modifies bitmap persistence on
+    migration.
     """
 
     src_node_name = 'node-a'
@@ -674,7 +675,8 @@ class TestAliasTransformMigration(TestDirtyBitmapMigration):
         bitmaps = self.vm_b.query_bitmaps()
 
         for node in bitmaps:
-            bitmaps[node] = sorted(((bmap['name'], bmap['persistent']) for bmap in bitmaps[node]))
+            bitmaps[node] = sorted(((bmap['name'], bmap['persistent'])
+                                    for bmap in bitmaps[node]))
 
         self.assertEqual(bitmaps,
                          {'node-a': [('bmap-a', True), ('bmap-b', False)],