Fix for containerd to use katello container repo

Create a script, this can easily be ported/re-written, I used /usr/local/bin/get_real_filename 

#!/bin/bash
while read line ; do
    abs_path="$(readlink "${line}")"
    echo "processing ${line}" >> /tmp/log
    if [ -n "${abs_path}" ] ; then
        stdbuf --output=0 echo "$(basename "${abs_path}")"
    else
        stdbuf --output=0 echo 'NULL'
    fi
done

sudo chmod 755 "/usr/local/bin/get_real_filename"
sudo chown root:root "/usr/local/bin/get_real_filename"


# In every virtualhost, (443 and 5000) add these lines around the top part:

# Set up rewrite map to look up real file names for sha256 sums for Docker-Content-Digest
RewriteEngine On
RewriteMap symlink "prg:/usr/local/bin/get_real_filename" apache:apache


# In pulp_docker.conf Under <Directory /var/www/pub/docker/v2/web/*/manifests/2>, around the other Headers

   RewriteCond %{REQUEST_FILENAME} -l
   RewriteCond ${symlink:%{REQUEST_FILENAME}} "(.+)"
   RewriteRule "(.*)" - [E=DIGEST:%1]
   Header set Docker-Content-Digest "%{DIGEST}e"