Endpoint /MAAS/api/1.0/files/?op=list returns HTTP 500 with juju-core.

[Impact]

- Trying to reach API endpoint /MAAS/api/1.0/files/?op=list returns HTTP 500.

[Test Case]

1) Run juju bootstrap over the maas environement

$ juju bootstrap --upload-tools -e maas
   - Output: ERROR gomaasapi: got error back from server: 500 Internal Server Error

2) Check the apache access logs:
192.168.122.1 - - [07/Apr/2014:22:26:45 +0000] "GET /MAAS/api/1.0/files/41793ac4-de01-4d20-860a-c9c0ac7a20ba-provider-state/ HTTP/1.1" 404 276 "-" "Go 1.1 package http"

192.168.122.1 - - [07/Apr/2014:22:26:48 +0000] "GET /MAAS/api/1.0/files/?op=list&prefix=41793ac4-de01-4d20-860a-c9c0ac7a20ba-tools%2Freleases%2Fjuju- HTTP/1.1" 500 642 "-" "Go 1.1 package http"

3) Apache error logs:

  [Mon Apr 07 22:26:49 2014] [error] [client 192.168.122.1] Premature end of script headers: wsgi.py

No further traceback information has been generated.

[Environment]

Ubuntu version:

lsb_release -a
No LSB modules are available.
Distributor ID: Ubuntu
Description: Ubuntu 12.04.4 LTS
Release: 12.04
Codename: precise

Maas package:

Version: 1.4+bzr1693+dfsg-0ubuntu2.3~ctools0

Juju package:

Version: 1.16.3-0ubuntu0.13.10.1