Add new #docker_exec for QA::Service::Omnibus

qa/qa/service/omnibus.rb

@@ -9,11 +9,12 @@ module QA
       end
 
       def gitlab_ctl(command, input: nil)
-        if input.nil?
-          shell "docker exec #{@name} gitlab-ctl #{command}"
-        else
-          shell "docker exec #{@name} bash -c '#{input} | gitlab-ctl #{command}'"
+        docker_exec("gitlab-ctl #{command}", input: input)
       end
+
+      def docker_exec(command, input: nil)
+        command = "#{input} | #{command}" if input
+        shell "docker exec #{@name} bash -c '#{command}'"
       end
     end
   end