CASC-231 HttpsURLConnectonFactory is Not Serializable

Problem: THe HttpsURLConnectionFactory is not serializable, causing problems for clients that must serialize
the principal (which depends on a ProxyRetriever).

Solution: Make the HttpsURLConnectionFactory serializable.

QA Notes: added unit test to confirm serialize-deserialize
It may not be a practical issue here, but generally, they lead to namespace collisions. (Also, at some point, I suppose this type of thing had a negative effect on classloading, but now, everything is lazily loaded anyway). 

Also there are java.net imports below that are explicit.