Add a test app endpoint to list a directory.
Add a test app endpoint to list a directory.

Signed-Off-By: Todd Ritchie <14053b6112ba5a4564ab1eef2c7f6dcce9f47ffd@pivotal.io>

cf-platform-eng/tile-generator,cf-platform-eng/tile-generator,cf-platform-eng/tile-generator,cf-platform-eng/tile-generator