MINIFICPP-915 - add util to list all of a directory without callback

Signed-off-by: Arpad Boda <aboda@apache.org>

This closes #640

libminifi/include/utils/file/FileUtils.h

@@ -19,6 +19,7 @@
 
 #include <sstream>
 #include <fstream>
+#include <vector>
 #ifdef BOOST_VERSION
 #include <boost/filesystem.hpp>
 #else
@@ -402,6 +403,20 @@ class FileUtils {
 #endif
   }
 
+  static std::vector<std::pair<std::string, std::string>> list_dir_all(const std::string& dir, const std::shared_ptr<logging::Logger> &logger,
+                                                                       bool recursive = true)  {
+
+    std::vector<std::pair<std::string, std::string>> fileList;
+    auto lambda = [&fileList] (const std::string &path, const std::string &filename) {
+      fileList.push_back(make_pair(path, filename));
+      return true;
+    };
+
+    list_dir(dir, lambda, logger, recursive);
+
+    return fileList;
+  }
+
   /*
    * Provides a platform-independent function to list a directory
    * Callback is called for every file found: first argument is the path of the directory, second is the filename