Simplify specs for new Redis instance

- Introduce redis_new_instance_shared_examples

lib/gitlab/health_checks/redis/redis_abstract_check.rb

@@ -13,7 +13,7 @@ module Gitlab
         private
 
         def redis_instance_class_name
-          Gitlab::Redis.const_get(redis_instance_name.camelize , false)
+          Gitlab::Redis.const_get(redis_instance_name.camelize, false)
         end
 
         def metric_prefix

spec/lib/gitlab/health_checks/redis/redis_check_spec.rb

@@ -4,5 +4,5 @@ require 'spec_helper'
 require_relative '../simple_check_shared'
 
 RSpec.describe Gitlab::HealthChecks::Redis::RedisCheck do
-  include_examples 'simple_check', 'redis_ping', 'Redis', 'PONG'
+  include_examples 'simple_check', 'redis_ping', 'Redis', true
 end