DCP: Set sticky bit for folder and secure delete

lib/runner/strategy/docker_container_pool.rb

@@ -47,7 +47,7 @@ class Runner::Strategy::DockerContainerPool < Runner::Strategy
         end
       end
     end
-    FileUtils.chmod_R('+rwX', local_workspace_path)
+    FileUtils.chmod_R('+rwtX', local_workspace_path)
   end
 
   def destroy_at_management

spec/lib/runner/strategy/docker_container_pool_spec.rb

@@ -106,7 +106,7 @@ describe Runner::Strategy::DockerContainerPool do
     end
 
     it 'sets permission bits on the workspace' do
-      expect(FileUtils).to receive(:chmod_R).with('+rwX', local_path)
+      expect(FileUtils).to receive(:chmod_R).with('+rwtX', local_path)
       container_pool.copy_files(files)
     end