Running apt-get clean before an update/install should help to prevent
failures during installation. This will help to improve the build
stability.

Source:
 - https://stackoverflow.com/questions/35923576/debian-httpredir-mirror-system-unreliable-unusable-in-docker

Change-Id: Id7d6ee95cfec28af59311b4d9e6852ae5e5e4c8c
Tuleap: #873