Replace deprecated with_lockmode with with_for_update

The Query.with_lockmode() method is deprecated since version 0.9.0
and will be removed in a future release. [1]
This patch replaces it with Query.with_for_update().
The 'faultstring' was been modified to 'Exactly 5 or 6 columns has to be
specified for iterator expression', so adds one space between "iterator"
and "expression" for 'expected_error_msg'.

Also use upper-constraints in doc build to avoid issues in pdf build.

[1]
https://docs.sqlalchemy.org/en/13/orm/query.html#sqlalchemy.orm.query.Query.with_lockmode

Closes-Bug: #1933226
Change-Id: I0ad514da647bb08790259fd27e56a41f6dbbbaa0

tox.ini

@@ -49,7 +49,9 @@ commands =
 
 [testenv:docs]
 setenv = PYTHONHASHSEED=0
-deps = -r{toxinidir}/doc/requirements.txt
+deps =
+  -c{env:UPPER_CONSTRAINTS_FILE:https://releases.openstack.org/constraints/upper/master}
+  -r{toxinidir}/doc/requirements.txt
 commands =
   rm -fr doc/build doc/source/api/ .autogenerated
   sphinx-build -W --keep-going -b html doc/source doc/build/html