add EVAL_RO & EVALSHA_RO

[xiaobiaozhao]

1. Each worker thread contains a Lua VM, the Lua VM shared with all connections on this thread. This VM specifically executes the EVAL_RO command.
2. Each connection's commends is pipeline runing.
3. Each worker's connetions send a lot of commands to kvrocks at the same time, but the same thread will exec command one by one. So the same thread can share one Lua VM.

[git-hulk]

Cool, it's good to separate the Lua vm to improve the performance in the readonly mode.
You can go ahead implementing this if you're willing to do this.