add rhncheck

- this script will check if the certs defined for cdn.redhat.com
  repositories are valid
- if the certs are not valid, the script will download new certs
  from redhat and perform another check against the newly downloaded certs
- an email is sent containing all repositories that have issues, including
  an attachment of the new cert should one exist
- .gitlab-ci, generatejobs have been 'tweaked' to support this 'non reposync'
  workflow