cerebro-uninstalled: 404 when trying to download zlib-1.2.10.tar.xz

EDIT: This issue should maybe have been opened for https://github.com/EricssonResearch/cerbero.

I'm trying to [build for Linux](https://github.com/EricssonResearch/openwebrtc/wiki/Building-OpenWebRTC), but the command `./cerbero-uninstalled -c config/linux.cbc fetch-package --full-reset --reset-rdeps openwebrtc` is failing because https://gstreamer.freedesktop.org/src/mirror/zlib-1.2.10.tar.xz doesn't exist anymore. It looks like gstreamer is now distributing tar.gz files instead of not tar.xz files, because https://gstreamer.freedesktop.org/src/mirror/zlib-1.2.10.tar.gz exists.

Additionally, http://zlib.net/zlib-1.2.10.tar.xz doesn't exist, but http://zlib.net/zlib-1.2.11.tar.xz does. Maybe consider using the file from their archive, like http://zlib.net/fossils/zlib-1.2.10.tar.gz, which won't get removed when new versions are released.

Here's the full output:

```
vor ~/job/cerbero $ ./cerbero-uninstalled -c config/linux.cbc fetch-package --full-reset --reset-rdeps openwebrtc
WARNING: Using default configuration because /home/martin/.cerbero/cerbero.cbc is missing
Fetching the following recipes: libffi glib orc zlib bzip2 openssl gobject-introspection libjpeg-turbo libpng gstreamer-1.0 gst-plugins-base-1.0 gst-plugins-good-1.0 gst-plugins-bad-1.0 opus libvpx openh264 graphene libsrtp libnice libunwind gstreamer-1.0-static gst-plugins-base-1.0-static gst-plugins-good-1.0-static gst-plugins-bad-1.0-static libnice-static openwebrtc openwebrtc-gst-plugins libusrsctp seed javascriptcoregtk icu openwebrtc-gst-plugins-static
[(1/32) libffi -> Fetch ]
fatal: remote origin already exists.
Fetching origin
HEAD is now at 60e4250 make executable
[(2/32) glib -> Fetch ]
-----> Fetching tarball http://ftp.acc.umu.se/pub/GNOME/sources/glib/2.50/glib-2.50.2.tar.xz to /home/martin/job/cerbero/build/sources/local/glib-2.50.2/glib-2.50.2.tar.xz
File /home/martin/job/cerbero/build/sources/local/glib-2.50.2/glib-2.50.2.tar.xz already downloaded.
[(3/32) orc -> Fetch ]
fatal: remote origin already exists.
Fetching origin
HEAD is now at db333e1 Back to development
[(4/32) zlib -> Fetch ]
-----> Fetching tarball http://zlib.net/zlib-1.2.10.tar.xz to /home/martin/job/cerbero/build/sources/local/zlib-1.2.10/zlib-1.2.10.tar.xz
Downloading http://zlib.net/zlib-1.2.10.tar.xz
--2017-04-28 09:55:03-- http://zlib.net/zlib-1.2.10.tar.xz
Resolving zlib.net... 69.73.132.10
Connecting to zlib.net|69.73.132.10|:80... connected.
HTTP request sent, awaiting response... 404 Not Found
2017-04-28 09:55:03 ERROR 404: Not Found.

Downloading https://gstreamer.freedesktop.org/src/mirror/zlib-1.2.10.tar.xz
--2017-04-28 09:55:03-- https://gstreamer.freedesktop.org/src/mirror/zlib-1.2.10.tar.xz
Loaded CA certificate '/etc/ssl/certs/ca-certificates.crt'
Resolving gstreamer.freedesktop.org... 131.252.210.176, 2610:10:20:722:a800:ff:feda:470f
Connecting to gstreamer.freedesktop.org|131.252.210.176|:443... connected.
HTTP request sent, awaiting response... 404 Not Found
2017-04-28 09:55:04 ERROR 404: Not Found.

Traceback (most recent call last):
File "./cerbero/main.py", line 105, in run_command
res = commands.run(command, self.config, self.args)
File "./cerbero/commands/__init__.py", line 78, in run
return _commands[command].run(config, args)
File "./cerbero/commands/fetch.py", line 121, in run
args.print_only)
File "./cerbero/commands/fetch.py", line 61, in fetch
recipe.fetch()
File "./cerbero/build/source.py", line 134, in fetch
overwrite=redownload)
File "./cerbero/utils/shell.py", line 255, in download
raise e
FatalError
***** Error running 'fetch-package' command:

usage: cerbero-uninstalled [-h] [-c CONFIG]
{add-recipe,rdeps,tag,genxcconfig,genlibfiles,check,list-packages,show-config,add-package,build,genvsprops,shell,run,cleanone,packageinfo,bundle-source,buildone,wipe,debug-packages,package,bootstrap,list,checkpac
kage,deps,gensdkshell,fetch-package,fetch}
...
```

Start by locating the zlib recipe used by the cerbero-uninstalled fetch-package command and trace its download configuration through cerbero/commands/fetch.py and cerbero/build/source.py. Reproduce the failed zlib-1.2.10 fetch, then verify that the selected archive URL downloads successfully and the openwebrtc dependency fetch completes.

Written by the indexing model from the issue text.