Fix missing templating block for kolla-toolbox.

Change-Id: I4ce8244a3fb034493a75f4096de2640e11b48931
Closes-Bug: #1931867
(cherry picked from commit fb218ff)

Author: gtherond

docker/kolla-toolbox/Dockerfile.j2

@@ -72,10 +72,12 @@ LABEL maintainer="{{ maintainer }}" name="{{ image_name }}" build-date="{{ build
         'virtualenv'
     ] %}
 
+{% block kolla_toolbox_upper_constraints %}
 RUN mkdir -p /requirements \
     && curl -sSL -o /requirements/upper-constraints.txt https://releases.openstack.org/constraints/upper/{{ openstack_release }} \
     && {{ macros.install_pip(kolla_toolbox_pip_virtualenv_packages | customizable("pip_virtualenv_packages")) }} \
     && virtualenv --system-site-packages {{ virtualenv_path }}
+{% endblock %}
 
 ENV PATH {{ virtualenv_path }}/bin:$PATH
 

releasenotes/notes/add_kolla-toolbox_templating_block-3d284d886816e95a.yml

@@ -0,0 +1,5 @@
+---
+features:
+  - |
+    Add templating block for kolla-toolbox image helping to customize
+    upper-constraints URL used at build time for offline build scenario.