[webui] invalidate session in LDAP mode

found and fixed by Srinidhi B S

src/api/app/controllers/webui/user_controller.rb

@@ -14,6 +14,7 @@ def index
 
   def logout
     logger.info "Logging out: #{session[:login]}"
+    Rails.cache.delete("ldap_cache_userpasswd:#{session[:login]}")
     reset_session
     User.current = nil
     if CONFIG['proxy_auth_mode'] == :on