chore: construct images for combinations of stretch/buster, py{27,35,37}

Dockerfile.getversion

 ARG DIST
+ARG PYTHON
 FROM debian:$DIST-slim
 RUN apt-get update && \
     apt-get -y --no-install-recommends install \
@@ -10,4 +11,4 @@ RUN echo "deb http://apt.logilab.fr $DIST main" > /etc/apt/sources.list.d/logila
 RUN wget -O - https://apt.logilab.fr/key.asc | apt-key --keyring /etc/apt/trusted.gpg.d/logilab.gpg add -
 
 CMD apt-get update > /dev/null && \
-    apt-cache show python3-cubicweb | grep  '^Version' | cut -f2 -d' '
+    apt-cache show "$PYTHON"-cubicweb | grep  '^Version' | cut -f2 -d' '

build.py

@@ -136,38 +136,40 @@ def build_buildpackage(dist):
                '--build-arg', 'DIST={}'.format(dist),
                '-f', 'Dockerfile.buildpackage', '.')
 
-def get_cubicweb_images(debian_dists: list[str]):
+def get_cubicweb_images(debian_dists: list[str], python_versions: list[str]):
     images = []
     for dist in debian_dists:
-        check_call(
-            'docker',
-            'build',
-            '.',
-            '-f',
-            'Dockerfile.getversion',
-            '-t',
-            'cubicweb:getversion',
-            '--build-arg',
-            f'DIST={dist}'
-        )
-        versions = check_output(
-            'docker', 'run', '--rm', 'cubicweb:getversion'
-        ).splitlines()
-
-        # filter release candidate version
-        valid_versions = [
-            version for version in versions if '~rc' not in version
-        ]
-
-        images = []
-        for version in valid_versions:
-            image = CubicWebImage(
-                python='py37',
-                debian=dist,
-                package_name='python3-cubicweb',
-                package_version=version
+        for python_version in python_versions:
+            python = 'python' if python_version == 'py27' else 'python3'
+            check_call(
+                'docker',
+                'build',
+                '.',
+                '-f',
+                'Dockerfile.getversion',
+                '-t',
+                'cubicweb:getversion',
+                '--build-arg',
+                f'DIST={dist}',
+                '--build-arg',
+                f"PYTHON={python}"
             )
-            images.append(image)
+            versions = check_output(
+                'docker', 'run', '--rm', 'cubicweb:getversion'
+            ).splitlines()
+
+            # filter release candidate version
+            valid_versions = [
+                version for version in versions if '~rc' not in version
+            ]
+            for version in valid_versions:
+                image = CubicWebImage(
+                    python=python_version,
+                    debian=dist,
+                    package_name=f'{python}-cubicweb',
+                    package_version=version
+                )
+                images.append(image)
     return images
 
 def build(debian_dists, images=[], rebuild=False):
@@ -229,7 +231,9 @@ if __name__ == '__main__':
         help='push images')
     args = parser.parse_args()
     REGISTRY = args.registry
-    images = get_cubicweb_images(["stretch", "buster"])
+    images = get_cubicweb_images(["stretch", "buster"], ["py27"])
+    images += get_cubicweb_images(["stretch"], ["py35"])
+    images += get_cubicweb_images(["buster"], ["py37"])
     if args.push:
         push()
     else: