(SERVER-218) Docs on SSL server cert change and virtual ips

This commit includes some documentation related to the issue discovered
in SERVER-207 - the JDK assertion made that the server certificate does
not change following a session resumption attempt and a renegotiation
attempted from servers behind a virtual ip address.
This wording seems like it's not 100% clear; it seems like it needs to include a phrase like 'load-balanced' or 'VIP', because without that, it kind of sounds like we will only be able to ever connect to servers that have the same cert (so, e.g., it kind of implies that your puppetdb, classifier, etc. nodes must all have the same cert.)