Better error message from the lua script

[donaldong]

Sometimes we see errors such as

Redis::CommandError: ERR Error running script (call to f_5aca618019854a1275397a2ec745a306fa8d8fc9): @user_script:113: @user_script: 113: Wrong number of args calling Redis command From Lua script
from /home/dev/.rbenv/versions/2.5.5/lib/ruby/gems/2.5.0/gems/redis-4.1.3/lib/redis/client.rb:126:in `call'

This is not easy to debug. We don't know which script is it, nor do we know the real offending line since the Lua files are only templates.

It'd be nice to improve the error message so it's easier to debug.