Drop support for Python 3.6

Drop support for Python 3.6 as it's EOL and the current version of the
IBM cloud SDK requires 3.7+.

Change-Id: Icdac247e36568ae1372188000914fa00ee071baf

.zuul.yaml

@@ -231,11 +231,10 @@
           DIB_SIMPLE_INIT_NETWORKMANAGER: '1'
 
 - job:
-    name: nodepool-tox-py36
+    name: nodepool-tox-py38
     description: |
       Nodepool unit tests with ZooKeeper running
-    parent: tox-py36
-    nodeset: ubuntu-bionic
+    parent: tox-py38
     pre-run: playbooks/nodepool-tox/pre.yaml
     vars: &nodepool_tox_vars
       tox_environment:
@@ -243,14 +242,6 @@
         NODEPOOL_ZK_CERT: /opt/zookeeper/ca/certs/client.pem
         NODEPOOL_ZK_KEY: /opt/zookeeper/ca/keys/clientkey.pem
 
-- job:
-    name: nodepool-tox-py38
-    description: |
-      Nodepool unit tests with ZooKeeper running
-    parent: tox-py38
-    pre-run: playbooks/nodepool-tox/pre.yaml
-    vars: *nodepool_tox_vars
-
 - job:
     name: nodepool-tox-py39
     description: |
@@ -269,7 +260,6 @@
         - nodepool-build-image-siblings
         - zuul-tox-docs
         - tox-pep8
-        - nodepool-tox-py36
         - nodepool-tox-py38
         - nodepool-tox-py39
         - nodepool-functional-container-openstack-release
@@ -285,7 +275,6 @@
         - nodepool-upload-image
         - zuul-tox-docs
         - tox-pep8
-        - nodepool-tox-py36
         - nodepool-tox-py38
         - nodepool-tox-py39
         - nodepool-functional-k8s

setup.cfg

@@ -6,7 +6,7 @@ description-file =
 author = Zuul Team
 author-email = zuul-discuss@lists.zuul-ci.org
 home-page = https://zuul-ci.org/
-python-requires = >= 3.6
+python-requires = >= 3.7
 classifier =
     Intended Audience :: Information Technology
     Intended Audience :: System Administrators
@@ -14,7 +14,6 @@ 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