Drop support for Python 3.6, 3.7

Python 3.6 and Python 3.7 support has been dropped since Zed [1]. This
necessitates changes our jobs to build and publish docker images since
those currently use Python 3.6. We now use Python 3.9.

[1] https://governance.openstack.org/tc/reference/runtimes/zed.html

Change-Id: I228b7ff6691a025f1ba9b7d9449f294868942151
Co-authored-by: Stephen Finucane <stephenfin@redhat.com>

.zuul.yaml

@@ -189,8 +189,8 @@
     description: Build Docker images.
     allowed-projects: openstack/python-openstackclient
     requires:
-      - python-builder-3.7-container-image
-      - python-base-3.7-container-image
+      - python-builder-3.9-container-image
+      - python-base-3.9-container-image
     provides: osc-container-image
     vars: &osc_image_vars
       docker_images:
@@ -203,8 +203,8 @@
     description: Build Docker images and upload to Docker Hub.
     allowed-projects: openstack/python-openstackclient
     requires:
-      - python-builder-3.7-container-image
-      - python-base-3.7-container-image
+      - python-builder-3.9-container-image
+      - python-base-3.9-container-image
     provides: osc-container-image
     secrets:
       - name: docker_credentials

Dockerfile

@@ -13,12 +13,12 @@
 # See the License for the specific language governing permissions and
 # limitations under the License.
 
-FROM docker.io/opendevorg/python-builder:3.7 as builder
+FROM docker.io/opendevorg/python-builder:3.9 as builder
 
 COPY . /tmp/src
 RUN assemble
 
-FROM docker.io/opendevorg/python-base:3.7
+FROM docker.io/opendevorg/python-base:3.9
 
 COPY --from=builder /output/ /output
 RUN /output/install-from-bindep

setup.cfg

@@ -6,7 +6,7 @@ description_file =
 author = OpenStack
 author_email = openstack-discuss@lists.openstack.org
 home_page = https://docs.openstack.org/python-openstackclient/latest/
-python_requires = >=3.6
+python_requires = >=3.8
 classifier =
     Environment :: OpenStack
     Intended Audience :: Information Technology
@@ -15,8 +15,6 @@ classifier =
     Operating System :: POSIX :: Linux
     Programming Language :: Python
     Programming Language :: Python :: 3
-    Programming Language :: Python :: 3.6
-    Programming Language :: Python :: 3.7
     Programming Language :: Python :: 3.8
     Programming Language :: Python :: 3.9