Switch RedisCacheable to use Redis cache instance

This used the 'shared state' Redis due to an understandable
misunderstanding about the purpose of that. The shared state Redis is
for persistent data, and the cache Redis is for caching short-lived
data.

Despite the names, both the cache and the shared state instance are
available to all ways the Rails application is deployed (web nodes and
background job nodes in particular).

app/models/concerns/redis_cacheable.rb

@@ -26,7 +26,7 @@ module RedisCacheable
   end
 
   def cache_attributes(values)
-    Gitlab::Redis::SharedState.with do |redis|
+    Gitlab::Redis::Cache.with do |redis|
       redis.set(cache_attribute_key, values.to_json, ex: CACHED_ATTRIBUTES_EXPIRY_TIME)
     end
 
@@ -41,7 +41,7 @@ module RedisCacheable
 
   def cached_attributes
     strong_memoize(:cached_attributes) do
-      Gitlab::Redis::SharedState.with do |redis|
+      Gitlab::Redis::Cache.with do |redis|
         data = redis.get(cache_attribute_key)
         JSON.parse(data, symbolize_names: true) if data
       end

spec/models/ci/runner_spec.rb

@@ -270,7 +270,7 @@ describe Ci::Runner do
     it { is_expected.to eq([@runner2])}
   end
 
-  describe '#online?' do
+  describe '#online?', :clean_gitlab_redis_cache do
     let(:runner) { create(:ci_runner, :instance) }
 
     subject { runner.online? }
@@ -332,7 +332,7 @@ describe Ci::Runner do
     end
 
     def stub_redis_runner_contacted_at(value)
-      Gitlab::Redis::SharedState.with do |redis|
+      Gitlab::Redis::Cache.with do |redis|
         cache_key = runner.send(:cache_attribute_key)
         expect(redis).to receive(:get).with(cache_key)
           .and_return({ contacted_at: value }.to_json).at_least(:once)
@@ -640,7 +640,7 @@ describe Ci::Runner do
     end
 
     def expect_redis_update
-      Gitlab::Redis::SharedState.with do |redis|
+      Gitlab::Redis::Cache.with do |redis|
         redis_key = runner.send(:cache_attribute_key)
         expect(redis).to receive(:set).with(redis_key, anything, any_args)
       end
@@ -664,7 +664,7 @@ describe Ci::Runner do
       end
 
       it 'cleans up the queue' do
-        Gitlab::Redis::SharedState.with do |redis|
+        Gitlab::Redis::Cache.with do |redis|
           expect(redis.get(queue_key)).to be_nil
         end
       end

spec/models/concerns/redis_cacheable_spec.rb

@@ -31,7 +31,7 @@ describe RedisCacheable do
     subject { instance.cached_attribute(payload.each_key.first) }
 
     it 'gets the cache attribute' do
-      Gitlab::Redis::SharedState.with do |redis|
+      Gitlab::Redis::Cache.with do |redis|
         expect(redis).to receive(:get).with(cache_key)
           .and_return(payload.to_json)
       end
@@ -44,7 +44,7 @@ describe RedisCacheable do
     subject { instance.cache_attributes(payload) }
 
     it 'sets the cache attributes' do
-      Gitlab::Redis::SharedState.with do |redis|
+      Gitlab::Redis::Cache.with do |redis|
         expect(redis).to receive(:set).with(cache_key, payload.to_json, anything)
       end
 
@@ -52,7 +52,7 @@ describe RedisCacheable do
     end
   end
 
-  describe '#cached_attr_reader', :clean_gitlab_redis_shared_state do
+  describe '#cached_attr_reader', :clean_gitlab_redis_cache do
     subject { instance.name }
 
     before do