migrate-bitmaps-test: Fix pylint warnings

There are a couple of things pylint takes issue with:
- The "time" import is unused
- The import order (iotests should come last)
- get_bitmap_hash() doesn't use @self and so should be a function
- Semicolons at the end of some lines
- Parentheses after "if"
- Some lines are too long (80 characters instead of 79)
- inject_test_case()'s @name parameter shadows a top-level @name
  variable
- "lambda self: mc(self)" were equivalent to just "mc", but in
  inject_test_case(), it is not equivalent, so add a comment and disable
  the warning locally
- Always put two empty lines after a function
- f'exec: cat > /dev/null' does not need to be an f-string

Fix them.

Signed-off-by: Hanna Reitz <hreitz@redhat.com>
Message-Id: <20210902094017.32902-4-hreitz@redhat.com>
Reviewed-by: Vladimir Sementsov-Ogievskiy <vsementsov@virtuozzo.com>

tests/qemu-iotests/tests/migrate-bitmaps-test

@@ -20,11 +20,10 @@
 #
 
 import os
-import iotests
-import time
 import itertools
 import operator
 import re
+import iotests
 from iotests import qemu_img, qemu_img_create, Timeout
 
 
@@ -37,6 +36,12 @@ mig_cmd = 'exec: cat > ' + mig_file
 incoming_cmd = 'exec: cat ' + mig_file
 
 
+def get_bitmap_hash(vm):
+    result = vm.qmp('x-debug-block-dirty-bitmap-sha256',
+                    node='drive0', name='bitmap0')
+    return result['return']['sha256']
+
+
 class TestDirtyBitmapMigration(iotests.QMPTestCase):
     def tearDown(self):
         self.vm_a.shutdown()
@@ -62,21 +67,16 @@ class TestDirtyBitmapMigration(iotests.QMPTestCase):
             params['persistent'] = True
 
         result = vm.qmp('block-dirty-bitmap-add', **params)
-        self.assert_qmp(result, 'return', {});
+        self.assert_qmp(result, 'return', {})
-
-    def get_bitmap_hash(self, vm):
-        result = vm.qmp('x-debug-block-dirty-bitmap-sha256',
-                        node='drive0', name='bitmap0')
-        return result['return']['sha256']
 
     def check_bitmap(self, vm, sha256):
         result = vm.qmp('x-debug-block-dirty-bitmap-sha256',
                         node='drive0', name='bitmap0')
         if sha256:
-            self.assert_qmp(result, 'return/sha256', sha256);
+            self.assert_qmp(result, 'return/sha256', sha256)
         else:
             self.assert_qmp(result, 'error/desc',
-                            "Dirty bitmap 'bitmap0' not found");
+                            "Dirty bitmap 'bitmap0' not found")
 
     def do_test_migration_resume_source(self, persistent, migrate_bitmaps):
         granularity = 512
@@ -97,7 +97,7 @@ class TestDirtyBitmapMigration(iotests.QMPTestCase):
         self.add_bitmap(self.vm_a, granularity, persistent)
         for r in regions:
             self.vm_a.hmp_qemu_io('drive0', 'write %d %d' % r)
-        sha256 = self.get_bitmap_hash(self.vm_a)
+        sha256 = get_bitmap_hash(self.vm_a)
 
         result = self.vm_a.qmp('migrate', uri=mig_cmd)
         while True:
@@ -106,7 +106,7 @@ class TestDirtyBitmapMigration(iotests.QMPTestCase):
                 break
         while True:
             result = self.vm_a.qmp('query-status')
-            if (result['return']['status'] == 'postmigrate'):
+            if result['return']['status'] == 'postmigrate':
                 break
 
         # test that bitmap is still here
@@ -164,7 +164,7 @@ class TestDirtyBitmapMigration(iotests.QMPTestCase):
         self.add_bitmap(self.vm_a, granularity, persistent)
         for r in regions:
             self.vm_a.hmp_qemu_io('drive0', 'write %d %d' % r)
-        sha256 = self.get_bitmap_hash(self.vm_a)
+        sha256 = get_bitmap_hash(self.vm_a)
 
         if pre_shutdown:
             self.vm_a.shutdown()
@@ -214,16 +214,22 @@ class TestDirtyBitmapMigration(iotests.QMPTestCase):
             self.check_bitmap(self.vm_b, sha256 if persistent else False)
 
 
-def inject_test_case(klass, name, method, *args, **kwargs):
+def inject_test_case(klass, suffix, method, *args, **kwargs):
     mc = operator.methodcaller(method, *args, **kwargs)
-    setattr(klass, 'test_' + method + name, lambda self: mc(self))
+    # We want to add a function attribute to `klass`, so that it is
+    # correctly converted to a method on instantiation.  The
+    # methodcaller object `mc` is a callable, not a function, so we
+    # need the lambda to turn it into a function.
+    # pylint: disable=unnecessary-lambda
+    setattr(klass, 'test_' + method + suffix, lambda self: mc(self))
+
 
 for cmb in list(itertools.product((True, False), repeat=5)):
     name = ('_' if cmb[0] else '_not_') + 'persistent_'
     name += ('_' if cmb[1] else '_not_') + 'migbitmap_'
     name += '_online' if cmb[2] else '_offline'
     name += '_shared' if cmb[3] else '_nonshared'
-    if (cmb[4]):
+    if cmb[4]:
         name += '__pre_shutdown'
 
     inject_test_case(TestDirtyBitmapMigration, name, 'do_test_migration',
@@ -270,7 +276,8 @@ class TestDirtyBitmapBackingMigration(iotests.QMPTestCase):
         self.assert_qmp(result, 'return', {})
 
         # Check that the bitmaps are there
-        for node in self.vm.qmp('query-named-block-nodes', flat=True)['return']:
+        nodes = self.vm.qmp('query-named-block-nodes', flat=True)['return']
+        for node in nodes:
             if 'node0' in node['node-name']:
                 self.assert_qmp(node, 'dirty-bitmaps[0]/name', 'bmap0')
 
@@ -287,7 +294,7 @@ class TestDirtyBitmapBackingMigration(iotests.QMPTestCase):
         """
         Continue the source after migration.
         """
-        result = self.vm.qmp('migrate', uri=f'exec: cat > /dev/null')
+        result = self.vm.qmp('migrate', uri='exec: cat > /dev/null')
         self.assert_qmp(result, 'return', {})
 
         with Timeout(10, 'Migration timeout'):