simplify container spawn/link tests
simplify container spawn/link tests

no longer need to make a temporary directory, as setting up job dirs is done
via fake command runner

cloudfoundry-incubator/garden-linux,tsaleh/garden,cloudfoundry-incubator/garden,cloudfoundry-incubator/garden,shashidharatd/garden-linux,savaki/garden,tangfeixiong/garden,savaki/garden,shashidharatd/garden-linux,cloudfoundry-incubator/garden-linux,cloudfoundry-incubator/garden-linux,tangfeixiong/garden,shashidharatd/garden-linux,tsaleh/garden,shashidharatd/garden-linux