(TK-58) Add remaining default server support

This PR addresses a bug wherein `get-registered-endpoints`, `log-registered-endpoints`, `join`, and `override-webserver-settings!` were using a default server with a key of `:default` rather than the actual default server specified by the user. 
What was happening in this test case prior to your change?  It seems like `override-webserver-settings` was errantly using a server ID of `:default`, which isn't a valid server, so that should have caused something to blow up somewhere, right?  How was this test passing before?