Check and make changes to the voltha-lib-go for redis

Changes required:

• Make changes to the voltha services, VGC to have an option to set the type of KVStore
• test out with the redis.
• All the changes done are to be upstreamed to LF, including changes in the voltha-lib-go 
  As of now voltha uses ETCD as it s DB, and ETCD is very sensitie to restarts and disk slowness and reload of the data. Plan is to move to redis 

Voltha-lib-go already has the redis client which can be used.

Make change in the voltha repos inclduing VGC to take an option from helmcharts to choose the type of KVStore. Based on that the KVStore needs to be used.