LRU + cache conflicts prevention. (#104)

* LRU + cache conflicts prevention.

* Bugfix universalCache flooding ( issue #105 )

  1. Traefik cancels the context for old plugin instances
  2. Each plugin's Close() method is called
  3. The CacheInterfaceWrapper.Close() was calling cache.Close() on the shared singleton caches
  4. Each Close() triggered Clear() which logged "Cleared all items" at INFO level

universal_cache.go

@@ -436,7 +436,7 @@ func (c *UniversalCache) Clear() {
 	c.currentSize = 0
 	c.currentMemory = 0
 
-	c.logger.Infof("UniversalCache[%s]: Cleared all items", c.config.Type)
+	c.logger.Debugf("UniversalCache[%s]: Cleared all items", c.config.Type)
 }
 
 // Size returns the number of items in the cache