Document URL: 
https://docs.openshift.org/latest/admin_guide/ipsec.html (Sort of?)

Describe the issue: 
Downstream docs used to have a section similar to ^ but after we determined that the doc said you have to install libreswan 3.19+ (which was not provided by RHEL) we removed the docs. 

The upstream docs now make reference to the use of libreswan 3.15 (which IS provided by RHEL). As such I feel we need to document how to use 3.15 until 3.19+ is included in RHEL

I have spoken with the engineer who worked on this stuff and will be adding him to the bug shortly