rhel-atomic: set EOL dates
RHEL Atomic Host reached EOL on August 6, 2020; hence, add that EOL date to all the rhel-atomic versions.
https://access.redhat.com/documentation/en-us/red_hat_enterprise_linux_atomic_host/7/html/release_notes/index#deprecation_notice
https://access.redhat.com/solutions/4813941
https://bugzilla.redhat.com/show_bug.cgi?id=1765349
Signed-off-by: Pino Toscano ptoscano@redhat.com