[VOL-3860] redis client support in voltha-lib-go

redis client support has been added in this patch. There are two
types client `redis` and `redis-sentinel` to connect a redis instance.
redis-sentinel is required to be able to find the master redis
instance from a redis-sentinel process. See redis-sentinel usage
https://redis.io/topics/sentinel and
https://pkg.go.dev/github.com/go-redis/redis/v8#NewFailoverClient
for more information. If there is no need to have any failover
mechanism then the redis client type is the option to choose.

Change-Id: I997ed92115a9d565df632c6dd8184b9bab77b991
diff --git a/vendor/github.com/go-redis/redis/v8/.travis.yml b/vendor/github.com/go-redis/redis/v8/.travis.yml
new file mode 100644
index 0000000..1bf578d
--- /dev/null
+++ b/vendor/github.com/go-redis/redis/v8/.travis.yml
@@ -0,0 +1,20 @@
+dist: xenial
+language: go
+
+services:
+  - redis-server
+
+go:
+  - 1.14.x
+  - 1.15.x
+  - tip
+
+matrix:
+  allow_failures:
+    - go: tip
+
+go_import_path: github.com/go-redis/redis
+
+before_install:
+  - curl -sSfL https://raw.githubusercontent.com/golangci/golangci-lint/master/install.sh | sh -s --
+    -b $(go env GOPATH)/bin v1.31.0