fix schema migration hooks (partial) SQL Server requires some additional steps to alter columns (index drop and restore, etc...) and this in turn requires passing a connection on the DB to find out the indexes. Also partially fix an issue where the null_allowed value was not correctly computed. Still some problems in there (see https://www.logilab.net/cwo/ticket/1109558)

#!/usr/bin/env python
from cubicweb.cwctl import run
import sys
run(sys.argv[1:])