[alembic] Alembic operations require keywords only arguments

Since [1] (release 1.11.0), the Alembic operations "now enforce
keyword-only arguments as passed as keyword and not positionally"
(from the commit message).

This change is compatible with the previous versions (as confirmed
in the CI).

[1]zzzeek/alembic@df75e85

Closes-Bug: #2019948
Change-Id: I020585a192ec5bcfb92cf92ef235da379ccb985e

Author: ralonsoh

nova/db/main/migrations/versions/16f1fbcab42b_resolve_shadow_table_diffs.py

@@ -44,12 +44,14 @@ def upgrade():
     # 252_add_instance_extra_table; we shouldn't have created an index for the
     # shadow table
 
-    op.drop_index('shadow_instance_extra_idx', 'shadow_instance_extra')
+    op.drop_index(index_name='shadow_instance_extra_idx',
+                  table_name='shadow_instance_extra')
 
     # 373_migration_uuid; we shouldn't have created an index for the shadow
     # table
 
-    op.drop_index('shadow_migrations_uuid', 'shadow_migrations')
+    op.drop_index(index_name='shadow_migrations_uuid',
+                  table_name='shadow_migrations')
 
     # 298_mysql_extra_specs_binary_collation; we changed the collation on the
     # main table but not the shadow table