Enable serf encryption (#1791)

* Added the keygen command

* Added support for gossip encryption

* Changed the URL for keyring management

* Fixed the cli

* Added some tests

* Added tests for keyring operations

* Added a test for removal of keys

* Added some docs

* Fixed some docs

* Added general options

command/agent/config_parse.go

@@ -484,6 +484,7 @@ func parseServer(result **ServerConfig, list *ast.ObjectList) error {
 		"retry_max",
 		"retry_interval",
 		"rejoin_after_leave",
+		"encrypt",
 	}
 	if err := checkHCLKeys(listVal, valid); err != nil {
 		return err