constants: define ENGINE_METHOD_RSA

Original Commit Message:
  constants.ENGINE_METHOD_RSA was documented, but not implemented.

  PR-URL: nodejs#5463
  Reviewed-By: Fedor Indutny <fedor@indutny.com>

Backport-Of: nodejs#5463
PR-URL: nodejs#11002
Reviewed-By: Anna Henningsen <anna@addaleax.net>
Reviewed-By: James M Snell <jasnell@gmail.com>

src/node_constants.cc

@@ -864,6 +864,10 @@ void DefineOpenSSLConstants(Local<Object> target) {
 
 # ifndef OPENSSL_NO_ENGINE
 
+# ifdef ENGINE_METHOD_RSA
+    NODE_DEFINE_CONSTANT(target, ENGINE_METHOD_RSA);
+# endif
+
 # ifdef ENGINE_METHOD_DSA
     NODE_DEFINE_CONSTANT(target, ENGINE_METHOD_DSA);
 # endif