[Docs] Exception for MFA/smartcards
[Docs] Exception for MFA/smartcards

This patch adds documentation for RHEL-07-010500 that explains the needs
for an exception for MFA/smartcards.

Implements: blueprint security-rhel7-stig
Change-Id: Ibea2131940c7ebf32353e5132cf0eeea4cc29577

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