Apply default umask in SetupEnvironment()

This change makes all filesystem artifacts--files and directories--being
created with the default umask.

src/rpc/request.cpp

@@ -86,7 +86,7 @@ bool GenerateAuthCookie(std::string *cookie_out)
     std::string cookie = COOKIEAUTH_USER + ":" + HexStr(rand_pwd);
 
     /** the umask determines what permissions are used to create this file -
-     * these are set to 077 in init.cpp.
+     * these are set to 0077 in util/system.cpp.
      */
     std::ofstream file;
     fs::path filepath_tmp = GetAuthCookieFile(true);