Add centos7-rocky symlink for centos7-master
Add centos7-rocky symlink for centos7-master

It is useful to keep a symlink from the current in-progress release
(Rocky in this case) to master, since it simplifies some programmatic
access to the repos. This commit adds a centos7-rocky symlink for
centos7-master, which will move later on for the next release (Stein).

Change-Id: Ida717db31b4c4881c32b89d1554f050b8c1f7894

javierpena/puppet-delorean,rdo-infra/puppet-dlrn,rdo-infra/puppet-dlrn,javierpena/puppet-delorean,javierpena/puppet-delorean,rdo-infra/puppet-dlrn