Go - Increase idle connection pool to 5k

These were the peak QPS results I got on m1.large just now, from changing the idle connection limit from 100 to 5000 (to match the MySQL connection limit). 

I'm not sure the original motivation to set it so low, however, so perhaps I'm missing something. 


               w/5000     w/100
     query       7769      6633
      json      18363     18726
        db       8416      8189
    update       4252      4030
   fortune       3360      3295