Simplify functests job

At one point we had an array of functest jobs; we were testing
building on trusty, bionic, maybe centos, with python2 and python3.
The only thing left of all these combos these days is "bionic-python3"
(that's where this naming comes from).

We can remove the levels of abstraction now and just have the one job
to avoid confusion.

Change-Id: Id37d62a17f9b7f6dc6dc35585c29eddd435ce913

.zuul.d/jobs.yaml

@@ -13,11 +13,11 @@
       - ^doc/.*$
 
 - job:
-    name: dib-functests-default
+    name: dib-functests
     description: |
       This is the base set of stable tests
-    abstract: true
     parent: dib-functests-base
+    nodeset: ubuntu-bionic
     vars:
       dib_functests:
         - containerfile/focal-build-succeeds
@@ -44,15 +44,6 @@
         - centos-minimal/8-aarch64-build-succeeds
         - openeuler-minimal/20.03-LTS-SP2-build-succeeds
 
-# Bionic / Python3 tests
-- job:
-    name: dib-functests-bionic-python3
-    description: |
-      Run the default tests on a Bionic build host with Python 3
-    parent: dib-functests-default
-    nodeset: ubuntu-bionic
-
-
 # ARM64 tests
 - job:
     name: dib-functests-arm64-bionic

.zuul.d/project.yaml

@@ -11,7 +11,7 @@
     check:
       jobs:
         - openstack-tox-pylint
-        - dib-functests-bionic-python3
+        - dib-functests
         - opendev-buildset-registry
         - nodepool-build-image-siblings
         - dib-nodepool-functional-openstack-centos-7-src
@@ -50,7 +50,7 @@
         - dib-nodepool-functional-openstack-ubuntu-xenial-src
         - dib-nodepool-functional-openstack-ubuntu-bionic-src
         - dib-nodepool-functional-openstack-ubuntu-focal-src
-        - dib-functests-bionic-python3
+        - dib-functests
         - ironic-python-agent-check-image-dib-centos8
     experimental:
       jobs: