[centos6] update container for EOL

Change:
- Reference:
  https://lists.centos.org/pipermail/centos-devel/2020-December/056208.html
- Bump centos6 container to 1.25.0

Test Plan:
- ci_complete

Signed-off-by: Rick Elrod <rick@elrod.me>

changelogs/fragments/ansible-test-centos6-eol.yml

@@ -0,0 +1,2 @@
+minor_changes:
+  - ansible-test - centos6 end of life - container image updated to point to vault base repository (https://github.com/ansible/distro-test-containers/pull/54)

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

@@ -1,7 +1,7 @@
 default name=quay.io/ansible/default-test-container:2.9.0 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:1.7.0 python=3.6,2.6,2.7,3.5,3.7,3.8,3.9 seccomp=unconfined context=ansible-core
 alpine3 name=quay.io/ansible/alpine3-test-container:1.19.0 python=3.8
-centos6 name=quay.io/ansible/centos6-test-container:1.17.0 python=2.6 seccomp=unconfined
+centos6 name=quay.io/ansible/centos6-test-container:1.25.0 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:1.21.0 python=3.6 seccomp=unconfined
 fedora30 name=quay.io/ansible/fedora30-test-container:1.17.0 python=3.7