Set batch size to avoid cursor timeout during migration

closes #3654
https://pulp.plan.io/issues/3654

(cherry picked from commit 2bcbc35)

plugins/pulp_rpm/plugins/migrations/0033_checksums_and_templates.py

@@ -41,9 +41,9 @@ def migrate(*args, **kwargs):
     srpm_collection = db['units_srpm']
     drpm_collection = db['units_drpm']
 
-    for rpm in rpm_collection.find({}, ['checksum', 'checksumtype', 'repodata']):
+    for rpm in rpm_collection.find({}, ['checksum', 'checksumtype', 'repodata']).batch_size(100):
         migrate_rpm_base(rpm_collection, rpm)
-    for srpm in srpm_collection.find({}, ['checksum', 'checksumtype', 'repodata']):
+    for srpm in srpm_collection.find({}, ['checksum', 'checksumtype', 'repodata']).batch_size(100):
         migrate_rpm_base(srpm_collection, srpm)
 
     migrate_drpms(drpm_collection)

plugins/test/unit/plugins/migrations/test_0033_checksums_and_templates.py

@@ -18,9 +18,9 @@ def test_calls_migrate_rpm_base(self, mock_migrate_drpms, mock_migrate_rpm_base,
         mock_db = mock_get_db.return_value
         mock_unit = mock.MagicMock()
         mock_rpm_collection = mock_db['units_rpm']
-        mock_rpm_collection.find.return_value = [mock_unit]
+        mock_rpm_collection.find.return_value.batch_size.return_value = [mock_unit]
         mock_srpm_collection = mock_db['units_srpm']
-        mock_srpm_collection.find.return_value = [mock_unit]
+        mock_srpm_collection.find.return_value.batch_size.return_value = [mock_unit]
 
         migration.migrate()