apps:run test with lengthy output -- don't log actual output on failure

When/if this [apps:run test](https://github.com/deis/workflow-e2e/blob/b65bed77e653a083e7a32554709d19a7df9522e1/tests/apps_test.go#L218-L223) fails, the `Expect` statement proceeds to log the entire command's output, corrupting the user's terminal and crowding out logs with byte code.

We should re-jigger the test, perhaps checking first if the byte array does not match expected (outside of `Expect`) and then, if not, logging some standard error/failure message accordingly.