Centos 7 based jobs are failing on TASK [Enable container-tools and disable rhel-modules] with error: /bin/sh: line 1: dnf: command not found

Description:-

Centos 7 based jobs are failing on TASK [Enable container-tools and disable rhel-modules] with error: /bin/sh: line 1: dnf: command not found

So, far we have noticed this failure on the following jobs:-

periodic-tripleo-ci-centos-7-multinode-1ctlr-featureset037-updates-stein
periodic-tripleo-ci-centos-7-undercloud-containers-stein
periodic-tripleo-ci-centos-7-standalone-stein
periodic-tripleo-ci-centos-7-ovb-1ctlr_1comp-featureset002-stein-upload

Logs:-

https://logserver.rdoproject.org/openstack-periodic-integration-stable4-5/opendev.org/openstack/tripleo-ci/master/periodic-tripleo-ci-centos-7-undercloud-containers-stein/bfe9095/job-output.txt

~~~
2020-12-30 13:52:27.688114 | TASK [Enable container-tools and disable rhel-modules]
2020-12-30 13:52:28.020301 | primary | + dnf module disable container-tools:rhel8 -y
2020-12-30 13:52:28.020992 | primary | /bin/sh: line 1: dnf: command not found
2020-12-30 13:52:28.237860 | primary | ERROR
2020-12-30 13:52:28.238078 | primary | {
2020-12-30 13:52:28.238128 | primary | "delta": "0:00:00.006601",
2020-12-30 13:52:28.238166 | primary | "end": "2020-12-30 13:52:28.021627",
2020-12-30 13:52:28.238203 | primary | "msg": "non-zero return code",
2020-12-30 13:52:28.238239 | primary | "rc": 127,
2020-12-30 13:52:28.238274 | primary | "start": "2020-12-30 13:52:28.015026"
2020-12-30 13:52:28.238309 | primary | }
~~~

https://logserver.rdoproject.org/openstack-periodic-integration-stable4-5/opendev.org/openstack/tripleo-ci/master/periodic-tripleo-ci-centos-7-multinode-1ctlr-featureset037-updates-stein/6b64e59/job-output.txt

~~~
2020-12-30 14:02:08.467490 | TASK [Enable container-tools and disable rhel-modules]
2020-12-30 14:02:09.189305 | primary | + dnf module disable container-tools:rhel8 -y
2020-12-30 14:02:09.190093 | primary | /bin/sh: line 1: dnf: command not found
2020-12-30 14:02:09.233140 | secondary | + dnf module disable container-tools:rhel8 -y
2020-12-30 14:02:09.233973 | secondary | /bin/sh: line 1: dnf: command not found
2020-12-30 14:02:09.696696 | primary | ERROR
2020-12-30 14:02:09.696837 | primary | {
2020-12-30 14:02:09.696877 | primary | "delta": "0:00:00.006698",
2020-12-30 14:02:09.696910 | primary | "end": "2020-12-30 14:02:09.190754",
2020-12-30 14:02:09.696942 | primary | "msg": "non-zero return code",
2020-12-30 14:02:09.696972 | primary | "rc": 127,
2020-12-30 14:02:09.697001 | primary | "start": "2020-12-30 14:02:09.184056"
2020-12-30 14:02:09.697030 | primary | }
2020-12-30 14:02:09.851393 | secondary | ERROR
2020-12-30 14:02:09.851534 | secondary | {
2020-12-30 14:02:09.851572 | secondary | "delta": "0:00:00.008049",
2020-12-30 14:02:09.851603 | secondary | "end": "2020-12-30 14:02:09.234769",
2020-12-30 14:02:09.851655 | secondary | "msg": "non-zero return code",
2020-12-30 14:02:09.851690 | secondary | "rc": 127,
2020-12-30 14:02:09.851718 | secondary | "start": "2020-12-30 14:02:09.226720"
2020-12-30 14:02:09.851746 | secondary | }
~~~

Caused after merge by following patch:-

https://review.rdoproject.org/r/#/c/31439/4/playbooks/tripleo-rdo-base/container-login.yaml

Looks like we just need a condition here https://review.rdoproject.org/r/gitweb?p=config.git;a=blob;f=playbooks/tripleo-rdo-base/container-login.yaml#l11 to trigger on c8 only