Be explicit about python base image version

We have versioned base images now, use them.

Change-Id: Ia5da9327d4cc1e26293550202a9ae0a9951a77aa

.zuul.yaml

@@ -19,8 +19,8 @@
     parent: opendev-build-docker-image
     description: Build OpenDev Docker images for LodgeIt
     requires:
-      - python-base-container-image
-      - python-builder-container-image
+      - python-base-3.7-container-image
+      - python-builder-3.7-container-image
     provides: lodgeit-container-image
     vars: &lodgeit_opendev_image_vars
       zuul_work_dir: src/opendev.org/opendev/lodgeit
@@ -34,8 +34,8 @@
     parent: opendev-upload-docker-image
     description: Build OpenDev LodgeIt Docker images and upload to Docker Hub.
     requires:
-      - python-base-container-image
-      - python-builder-container-image
+      - python-base-3.7-container-image
+      - python-builder-3.7-container-image
     provides: lodgeit-container-image
     vars: *lodgeit_opendev_image_vars
     secrets:

Dockerfile

@@ -13,11 +13,11 @@
 # See the License for the specific language governing permissions and
 # limitations under the License.
 
-FROM opendevorg/python-builder as builder
+FROM opendevorg/python-builder:3.7 as builder
 COPY . /tmp/src
 RUN assemble
 
-FROM opendevorg/python-base as lodgeit
+FROM opendevorg/python-base:3.7 as lodgeit
 COPY --from=builder /output/ /output
 RUN /output/install-from-bindep