conn selection: chose the least used conneciton
conn selection: chose the least used conneciton

Chose the least used connection to return for a host, this will better
spread out queries amongst connections, which should help to reduce
stream exhaustion.

gus/gocql,mailgun/gocql,gus/gocql,Zariel/gocql,i/gocql,i/gocql,gocql/gocql,vrischmann/gocql,gocql/gocql,ChannelMeter/gocql,revinate/gocql,aai/gocql,znly/gocql,znly/gocql,ChannelMeter/gocql,mailgun/gocql,revinate/gocql,vrischmann/gocql,aai/gocql,Zariel/gocql