Add a storm-base image

Refactor storm image dependencies. Previously we had:

base -> storm -> monasca-thresh

Both storm and monasca-thresh images are final, and each includes a
footer. This causes issues when the footer expects to be at the end of
the image, or there to be only a single footer. In particular, since
I2592a736206eaec811290e9fbdbf2540c0518ffe, the footer used in CI jobs
reverts to the public package mirrors.

This change introduces a storm-base image, and refactors the dependency
chain:

base -> storm-base -> storm
base -> storm-base -> monasca-thresh

Related-Bug: #1902101

Change-Id: I53e8ba8d4baa4434cf3c49ed94d1f7cb44099bee
(cherry picked from commit 93204ecfec)

docker/monasca/monasca-thresh/Dockerfile.j2

@@ -1,10 +1,8 @@
-FROM {{ namespace }}/{{ image_prefix }}storm:{{ tag }}
+FROM {{ namespace }}/{{ image_prefix }}storm-base:{{ tag }}
 {% block labels %}
 LABEL maintainer="{{ maintainer }}" name="{{ image_name }}" build-date="{{ build_date }}"
 {% endblock %}
 
-USER root
-
 {% block monasca_thresh_header %}{% endblock %}
 
 {% import "macros.j2" as macros with context %}

docker/storm/storm-base/Dockerfile.j2

@@ -3,7 +3,7 @@ FROM {{ namespace }}/{{ image_prefix }}base:{{ tag }}
 LABEL maintainer="{{ maintainer }}" name="{{ image_name }}" build-date="{{ build_date }}"
 {% endblock %}
 
-{% block storm %}{% endblock %}
+{% block storm_base_header %}{% endblock %}
 
 {% import "macros.j2" as macros with context %}
 
@@ -52,7 +52,4 @@ ENV PYTHON={{ '/usr/bin/python' ~ distro_python_version }}
 COPY extend_start.sh /usr/local/bin/kolla_extend_start
 RUN chmod 755 /usr/local/bin/kolla_extend_start
 
-{% block storm_footer %}{% endblock %}
-{% block footer %}{% endblock %}
-
-USER storm
+{% block storm_base_footer %}{% endblock %}

docker/storm/storm/Dockerfile.j2

@@ -0,0 +1,13 @@
+FROM {{ namespace }}/{{ image_prefix }}storm-base:{{ tag }}
+{% block labels %}
+LABEL maintainer="{{ maintainer }}" name="{{ image_name }}" build-date="{{ build_date }}"
+{% endblock %}
+
+{% block storm_header %}{% endblock %}
+
+{% import "macros.j2" as macros with context %}
+
+{% block storm_footer %}{% endblock %}
+{% block footer %}{% endblock %}
+
+USER storm