Redis: Update helm tests

This updates the Redis helm test to use the redislabs/redis-py
image instead of the base ubuntu image, which allows for cleaning
up of the helm test entrypoint script. This was done to address
routine failures in the multinode periodic jobs, eg:
http://zuul.openstack.org/build/49a9627901514eeda40906c146b9a551

Change-Id: Ida0fd39d2c6d3908aca4cdb42d3a271c39ecc601

redis/templates/test/_redis_test.sh.tpl

@@ -6,7 +6,5 @@ echo "Print Environmental variables"
 echo $REDIS_HOST
 echo $REDIS_PORT
 echo $REDIS_DB
-apt-get update
-apt-get -y install python-pip
-yes w | pip install redis
+
 python /tmp/python-tests.py

redis/values.yaml

@@ -20,7 +20,7 @@
 images:
   tags:
     redis: docker.io/redis:4.0.1
-    helm_tests: docker.io/ubuntu
+    helm_tests: docker.io/redislabs/redis-py:latest
     dep_check: quay.io/stackanetes/kubernetes-entrypoint:v0.3.1
     image_repo_sync: docker.io/docker:17.07.0
   pull_policy: IfNotPresent