[cesu] Do not download unavailable documents

Some documents are not ready to be downloaded, and when trying to download
them it results in a 500 error.
When now apply the same logic as in the site to decide if a document should
be listed or not.
7 jobs for master in 17 minutes and 10 seconds (queued for 1 second)
Status Job ID Name Coverage
  Build
passed #29877
build:3

00:01:18

 
  Test
passed #29880
load-modules:3

00:02:14

passed #29878
pyflakes:3

00:02:29

passed #29879
pyflakes-strict:3

00:02:37

passed #29881
unittests:3

00:02:02

43.0%
failed #29882
allowed to fail
unittests-modules:3

00:11:59

42.0%
 
  Deploy
passed #29883
doc:3

00:01:19

 
Name Stage Failure
failed
unittests-modules:3 Test
        </head>
<body>
<h1>Error: 400 Bad Request</h1>
<p>Sorry, the requested URL <tt>'https://ci.weboob.org/api/v1/modules'</tt>
caused an error:</p>
<pre>Invalid JSON payload.</pre>
</body>
</html>
ERROR: Job failed: exit code 1