Honor SSL config settings for ValidatorSites:

FIXES: #2990

* refactor common SSL client setup
* enable SSL in unit-test http server
* add tests for SSLHTTPDownloader
* misc test refactoring

src/test/jtx/impl/envconfig.cpp

@@ -60,6 +60,7 @@ setupConfigForUnitTests (Config& cfg)
     cfg["port_ws"].set("admin", getEnvLocalhostAddr());
     cfg["port_ws"].set("port", port_ws);
     cfg["port_ws"].set("protocol", "ws");
+    cfg.SSL_VERIFY = false;
 }
 
 namespace jtx {