infra/perl: switch to using a reliable mirror

The mirror we currently use is not a mirror, it's the main archive.

It has a few shortcomings:
  - it might not contain all the versions of the modules we use,
  - it can be unavailable at times (like now, for example)

Switch to using a realmirror, that:
  - does a round-robin on the actual mirror, so availability is better
  - contains all versions of all modules (yes, mojolicious is there!)

As a consequence, switch mojolicious to use our standard mirror,

Signed-off-by: "Yann E. MORIN" <yann.morin.1998@free.fr>
Cc: François Perrad <francois.perrad@gadz.org>
Cc: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>