Add cluster tests

only pad db key counts when running extractInfoMetrics() the first time

Move  location of redisgo

Bump redigo to 2.0.0 for new paths

set default db_keys & db_keys_expiring value to 0 for all available databases

update Gopkg.toml, use new version of dep, update vendored files

on CONFIG error log Debugf() only

update build instructions

A couple of tweaks

adding a few more client and network metrics

Add slave offset metrics

Update glide.yaml

as we all know

Changes for exporting redis only metrics if needed

upgrade redigo to 1.1.0  for rediss://