step-registry: use centos:8 instead of tools

As originally done in #11247.
`tools` only exists in 4.5+ releases.

Author: bbguimaraes

ci-operator/step-registry/ipi/conf/aws/ipi-conf-aws-ref.yaml

@@ -1,6 +1,9 @@
 ref:
   as: ipi-conf-aws
-  from: tools
+  from_image:
+   namespace: origin
+   name: centos
+   tag: '8'
   commands: ipi-conf-aws-commands.sh
   resources:
     requests:

ci-operator/step-registry/ipi/conf/ipi-conf-ref.yaml

@@ -1,6 +1,9 @@
 ref:
   as: ipi-conf
-  from: tools
+  from_image:
+   namespace: origin
+   name: centos
+   tag: '8'
   commands: ipi-conf-commands.sh
   resources:
     requests: