* optmize: reused a Lua table of plugins.
* feature: supported to check the Lua source by command `make check`.
* bug: reinitialize the prometheus variable each time.
* bugfix: added the plugin load.
* test: added test cases for limit count.
* test: added Lua sleep at the end of init_worker.
left enough time for read data from etcd, otherwise worker maybe deal with request before get data from etcd.
* test: added no_shuffle();
