move `lib/ci/model.rb` into `lib/gitlab/ci/model.rb`

app/models/ci/group_variable.rb

 module Ci
   class GroupVariable < ActiveRecord::Base
-    extend Ci::Model
+    extend Gitlab::Ci::Model
     include HasVariable
     include Presentable
 

app/models/ci/pipeline.rb

 module Ci
   class Pipeline < ActiveRecord::Base
-    extend Ci::Model
+    extend Gitlab::Ci::Model
     include HasStatus
     include Importable
     include AfterCommitQueue

app/models/ci/pipeline_schedule.rb

 module Ci
   class PipelineSchedule < ActiveRecord::Base
-    extend Ci::Model
+    extend Gitlab::Ci::Model
     include Importable
 
     acts_as_paranoid

app/models/ci/pipeline_schedule_variable.rb

 module Ci
   class PipelineScheduleVariable < ActiveRecord::Base
-    extend Ci::Model
+    extend Gitlab::Ci::Model
     include HasVariable
 
     belongs_to :pipeline_schedule

app/models/ci/pipeline_variable.rb

 module Ci
   class PipelineVariable < ActiveRecord::Base
-    extend Ci::Model
+    extend Gitlab::Ci::Model
     include HasVariable
 
     belongs_to :pipeline

app/models/ci/runner.rb

 module Ci
   class Runner < ActiveRecord::Base
-    extend Ci::Model
+    extend Gitlab::Ci::Model
 
     RUNNER_QUEUE_EXPIRY_TIME = 60.minutes
     ONLINE_CONTACT_TIMEOUT = 1.hour

app/models/ci/runner_project.rb

 module Ci
   class RunnerProject < ActiveRecord::Base
-    extend Ci::Model
+    extend Gitlab::Ci::Model
 
     belongs_to :runner
     belongs_to :project

app/models/ci/stage.rb

 module Ci
   class Stage < ActiveRecord::Base
-    extend Ci::Model
+    extend Gitlab::Ci::Model
     include Importable
     include HasStatus
     include Gitlab::OptimisticLocking

app/models/ci/trigger.rb

 module Ci
   class Trigger < ActiveRecord::Base
-    extend Ci::Model
+    extend Gitlab::Ci::Model
 
     acts_as_paranoid
 

app/models/ci/trigger_request.rb

 module Ci
   class TriggerRequest < ActiveRecord::Base
-    extend Ci::Model
+    extend Gitlab::Ci::Model
 
     belongs_to :trigger
     belongs_to :pipeline, foreign_key: :commit_id

app/models/ci/variable.rb

 module Ci
   class Variable < ActiveRecord::Base
-    extend Ci::Model
+    extend Gitlab::Ci::Model
     include HasVariable
     include Presentable
 

lib/ci/model.rb

-module Ci
-  module Model
-    def table_name_prefix
-      "ci_"
-    end
-
-    def model_name
-      @model_name ||= ActiveModel::Name.new(self, nil, self.name.split("::").last)
-    end
-  end
-end

lib/gitlab/ci/model.rb

+module Gitlab
+  module Ci
+    module Model
+      def table_name_prefix
+        "ci_"
+      end
+
+      def model_name
+        @model_name ||= ActiveModel::Name.new(self, nil, self.name.split("::").last)
+      end
+    end
+  end
+end