[dbapi] fix connect backwards compat harder
Passing None as group and host should result in
"pyro:///cubicweb.appid", not "pyro://None/None.appid". Followup for
2091d275fe5c. Closes #2882666.
if not rql('CWConstraintType X WHERE X name "RQLUniqueConstraint"',
ask_confirm=False):
rql('INSERT CWConstraintType X: X name "RQLUniqueConstraint"',
ask_confirm=False)