tls: do not refer to secureOptions as flags

Its confusing to have multiple names for the same thing, use
secureOptions consistently.

PR-URL: nodejs#9800
Reviewed-By: Roman Reiss <me@silverwind.io>
Reviewed-By: Michael Dawson <michael_dawson@ca.ibm.com>

lib/_tls_common.js

@@ -12,9 +12,9 @@ var crypto = null;
 const binding = process.binding('crypto');
 const NativeSecureContext = binding.SecureContext;
 
-function SecureContext(secureProtocol, flags, context) {
+function SecureContext(secureProtocol, secureOptions, context) {
   if (!(this instanceof SecureContext)) {
-    return new SecureContext(secureProtocol, flags, context);
+    return new SecureContext(secureProtocol, secureOptions, context);
   }
 
   if (context) {
@@ -29,7 +29,7 @@ function SecureContext(secureProtocol, flags, context) {
     }
   }
 
-  if (flags) this.context.setOptions(flags);
+  if (secureOptions) this.context.setOptions(secureOptions);
 }
 
 exports.SecureContext = SecureContext;