mgmt: Reinitialize multicast faces and partially reload config file on HUP signal

The following elements from the config file are reloaded:
- effective user/group
- log levels
- multicast faces (enable/disable)
- security

Change-Id: I6ddf124702b30610dd0404d8fbaa9a9d800f02bf
Refs: #1584
diff --git a/core/logger-factory.hpp b/core/logger-factory.hpp
index b5aa31d..cbf7424 100644
--- a/core/logger-factory.hpp
+++ b/core/logger-factory.hpp
@@ -81,6 +81,9 @@
   LogLevel
   parseLevel(const std::string& level);
 
+  LogLevel
+  extractLevel(const ConfigSection& item, const std::string& key);
+
 private:
 
   typedef std::map<std::string, LogLevel> LevelMap;