caches: don't clear all cache keys on exit as we lost state for not-recycled workers

rhodecode/lib/rc_cache/cache_key_meta.py

@@ -40,8 +40,8 b' def free_cache_keys(*args):'
         try:
             for cache_proc in cache_keys_by_pid:
                 CacheKey.query().filter(CacheKey.cache_key.startswith(cache_proc)).delete()
+                cache_keys_by_pid.remove(cache_proc)
             Session().commit()
-            cache_keys_by_pid.clear()
         except Exception:
             log.warn('Failed to clear keys, exiting gracefully')