Description of problem:
Some time ago the /etc/sysconfig/docker file stopped containing the following lines:

# If you want to add your own registry to be used for docker search and docker
# pull use the ADD_REGISTRY option to list a set of registries, each prepended
# with --add-registry flag. The first registry added will be the first registry
# searched.
ADD_REGISTRY='--add-registry registry.access.redhat.com'

Instead, the following lines are there now:

# Do not add registries in this file anymore. Use /etc/containers/registries.conf
# from the atomic-registries package.

The docker client configuration RPM needs to adapt to this change. At present, its post-installation script runs the following command:

sed -i '/ADD_REGISTRY/s/=.*/='"'"'--add-registry cds.example.com:5000'"'"'/' /etc/sysconfig/docker

But this command has no effect with recent versions of docker as there's no pattern for sed to modify.

By default, /etc/containers/registries.conf reads:

[registries.search]
registries = ['registry.access.redhat.com']

So, if this exists, it must be changed.

Version-Release number of selected component (if applicable):
RHUI 3.0.4

How reproducible:
Always

Steps to Reproduce:
1. Add a docker registry to RHUI and sync it.
2. Create a docker configuration RPM and install it on a client.
3. Run docker pull <the ID of the added registry> on the client.


Actual results:
Output:
Trying to pull repository registry.access.redhat.com/<the ID> ...
unknown: Not Found

Expected results:
The "docker pull" command talks with your load balancer on port 5000, not with Red Hat's registry.

Additional info:
The atomic client configuration tarball is also affected. In general:

# grep -r ADD_REGISTRY /etc/
/etc/rhui/templates/ostree-conf.sh:sed -i '/ADD_REGISTRY/s/=.*/='"'"'--add-registry !CDS_HOSTNAME_PORT!'"'"'/' /etc/sysconfig/docker
/etc/rhui/templates/rh-client-config-docker.spec:sed -i '/ADD_REGISTRY/s/=.*/='"'"'--add-registry !CDS!'"'"'/' /etc/sysconfig/docker