- max_conns / idle / per host are now read from env-vars and have
defaults set to 1024 for both values
- logging / metrics are collected in the client transaction
rather than via defer (this may impact throughput)
- function cache moved to use RWMutex to try to improve latency
around locking when updating cache
- logging message added to show latency in running GetReplicas
because this was observed to increase in a linear fashion under
high concurrency
- changes tested against 3-node bare-metal 1.13 K8s cluster
with kubeadm

Signed-off-by: Alex Ellis (VMware) <alexellis2@gmail.com>