[tests] Bump container versions (#71518) (#71598)

Change:
- This pulls in python 3.9.0rc1

Test Plan:
- CI, hopefully

Signed-off-by: Rick Elrod <rick@elrod.me>
(cherry picked from commit db519bc17c)

changelogs/fragments/default-test-container160.yml

@@ -0,0 +1,2 @@
+minor_changes:
+  - ansible-test - default container now uses default-test-container 2.7.0 and ansible-base-test-container 1.6.0. This brings in Python 3.9.0rc1 for testing.

test/lib/ansible_test/_data/completion/docker.txt

@@ -1,5 +1,5 @@
-default name=quay.io/ansible/default-test-container:2.6.0 python=3.6,2.6,2.7,3.5,3.7,3.8,3.9 seccomp=unconfined context=collection
+default name=quay.io/ansible/default-test-container:2.7.0 python=3.6,2.6,2.7,3.5,3.7,3.8,3.9 seccomp=unconfined context=collection
-default name=quay.io/ansible/ansible-base-test-container:1.5.0 python=3.6,2.6,2.7,3.5,3.7,3.8,3.9 seccomp=unconfined context=ansible-base
+default name=quay.io/ansible/ansible-base-test-container:1.6.0 python=3.6,2.6,2.7,3.5,3.7,3.8,3.9 seccomp=unconfined context=ansible-base
 centos6 name=quay.io/ansible/centos6-test-container:1.17.0 python=2.6 seccomp=unconfined
 centos7 name=quay.io/ansible/centos7-test-container:1.17.0 python=2.7 seccomp=unconfined
 centos8 name=quay.io/ansible/centos8-test-container:1.17.0 python=3.6 seccomp=unconfined