Add exception for supported release check
Add exception for supported release check

This patch adds docs for RHEL-07-020240 and gives deployers
details on EOL dates for Ubuntu, CentOS and, Red Hat.

Implements: blueprint security-rhel7-stig
Change-Id: I0a8846cbc363c5438f9741ef681e1877e19da262

major/openstack-ansible-security,major/openstack-ansible-security