retain gitkeep file

Author: chinandrew

jhu/tests/conftest.py

@@ -16,7 +16,8 @@
 def run_as_module():
     # Clean receiving directory
     for fname in listdir("receiving"):
-        remove(join("receiving", fname))
+        if fname != ".gitkeep":
+            remove(join("receiving", fname))
 
     with mock_s3():
         # Create the fake bucket we will be using