Convert all raw files from cherrypy as a string.

BUG=chromium:285287
TEST=Ran stage / is_staged

Change-Id: I0f10083801bc8463959d1df86f1ae865b26d12e2
Reviewed-on: https://chromium-review.googlesource.com/168046
Reviewed-by: Chris Sosa <sosa@chromium.org>
Tested-by: Chris Sosa <sosa@chromium.org>
diff --git a/devserver.py b/devserver.py
index 4b32269..7d8fd55 100755
--- a/devserver.py
+++ b/devserver.py
@@ -388,8 +388,10 @@
     if not artifacts and not files:
       raise DevServerError('No artifacts specified.')
 
-    return (artifacts.split(',') if artifacts else [],
-            files.split(',') if files else [])
+    # Note we NEED to coerce files to a string as we get raw unicode from
+    # cherrypy and we treat files as strings elsewhere in the code.
+    return (str(artifacts).split(',') if artifacts else [],
+            str(files).split(',') if files else [])
 
   @cherrypy.expose
   def build(self, board, pkg, **kwargs):