[epoxy] Cache listener endpoint for after shutdown
[epoxy] Cache listener endpoint for after shutdown

Cache the EpoxyListener endpoint information so that it can be accessed
after socket shutdown for things like logging.

This resolves a sporadic unit test failure.

Minor adjustments to match style guide for things like private and
readonly.

Closes https://github.com/Microsoft/bond/pull/222

tstein/bond,Microsoft/bond,sapek/bond,gencer/bond,chwarr/bond,gencer/bond,gencer/bond,tstein/bond,Microsoft/bond,tstein/bond,sapek/bond,sapek/bond,gencer/bond,Microsoft/bond,chwarr/bond,Microsoft/bond,tstein/bond,sapek/bond,Microsoft/bond,jdubrule/bond,chwarr/bond,jdubrule/bond,jdubrule/bond,gencer/bond,chwarr/bond,sapek/bond,chwarr/bond,jdubrule/bond,jdubrule/bond,jdubrule/bond,sapek/bond,tstein/bond,Microsoft/bond,tstein/bond,chwarr/bond