Do not log that the logging configuration is invalid on every request

Instead, log those messages *everytime* a subsequent message is being
logged.

refs #8957

library/Icinga/Application/ApplicationBootstrap.php

@@ -511,12 +511,12 @@ abstract class ApplicationBootstrap
             try {
                 Logger::create($loggingConfig);
             } catch (ConfigurationError $e) {
-                Logger::error($e);
+                Logger::getInstance()->registerConfigError($e->getMessage());
 
                 try {
                     Logger::getInstance()->setLevel($loggingConfig->get('level', Logger::ERROR));
                 } catch (ConfigurationError $e) {
-                    Logger::error($e);
+                    Logger::getInstance()->registerConfigError($e->getMessage());
                 }
             }
         }

library/Icinga/Application/Logger.php

@@ -67,6 +67,13 @@ class Logger
      */
     protected $level;
 
+    /**
+     * Error messages to be displayed prior to any other log message
+     *
+     * @var array
+     */
+    protected $configErrors = array();
+
     /**
      * Create a new logger object
      *
@@ -128,6 +135,24 @@ class Logger
         return $this;
     }
 
+    /**
+     * Register the given message as config error
+     *
+     * Config errors are logged every time a log message is being logged.
+     *
+     * @param   mixed   $arg,...    A string, exception or format-string + substitutions
+     *
+     * @return  $this
+     */
+    public function registerConfigError()
+    {
+        if (func_num_args() > 0) {
+            $this->configErrors[] = static::formatMessage(func_get_args());
+        }
+
+        return $this;
+    }
+
     /**
      * Create a new logger object
      *
@@ -170,6 +195,10 @@ class Logger
     public function log($level, $message)
     {
         if ($this->writer !== null && $this->level <= $level) {
+            foreach ($this->configErrors as $error_message) {
+                $this->writer->log(static::ERROR, $error_message);
+            }
+
             $this->writer->log($level, $message);
         }
     }