pylint: Fix migration E1120 no-value-for-parameter

Pylint raises E1120 on all many of our migrations because the insert
call is missing the dml parameter:

  cinder/db/sqlalchemy/migrate_repo/versions/123_cinder_init.py:870:9:
  E1120: No value for argument 'dml' in method call
  (no-value-for-parameter)

The dml parameter is automatically added by sqlalchemy using a
decorator, like this:

    @util.dependencies("sqlalchemy.sql.dml")
    def insert(self, dml, values=None, inline=False, **kwargs):

This patch adds the decorator to the pyling configured
signature-mutators to remove these errors from incorrectly showing.

Change-Id: Icbc72b3655f379c9b97134e68a425dc1d623dc7b

.pylintrc

@@ -222,7 +222,7 @@ additional-builtins=_
 [TYPECHECK]
 # List of module names for which member attributes should not be checked
 ignored-modules=six.moves,_MovedItems
-signature-mutators=unittest.mock.patch,unittest.mock.patch.object
+signature-mutators=unittest.mock.patch,unittest.mock.patch.object,sqlalchemy.util._preloaded.dependencies
 
 # This is for cinder.objects.*, and requests.packages.*, but due to
 # https://github.com/PyCQA/pylint/issues/2498