Landings (hence deployments) are blocked if a network resource becomes unavailable

[Vincent Ladeuil]

Out of the blue pygooglechart couldn't be installed on jenkins:

 https://jenkins.ubuntone.info/job/software-center-agent-merges/22/console

For a (yet) unknown reason we get a 403 when trying to download the source:

06:36:36 O: Downloading/unpacking pygooglechart (from -r requirements.txt (line 20))
06:36:36 O: HTTP error 403 while getting http://pygooglechart.slowchop.com/files/download/pygooglechart-0.3.0.tar.gz (from https://pypi.python.org/simple/pygooglechart/)
06:36:36 O: Could not install requirement pygooglechart (from -r requirements.txt (line 20)) because of error HTTP Error 403: Forbidden
06:36:37 O: Could not install requirement pygooglechart (from -r requirements.txt (line 20)) because of HTTP error HTTP Error 403: Forbidden for URL http://pygooglechart.slowchop.com/files/download/pygooglechart-0.3.0.tar.gz (from https://pypi.python.org/simple/pygooglechart/)

This blocks the landing of merge proposals which in turn blocks deployments.