utils/genrandconfig: use --no-check-certificate in wget by default

utils/genrandconfig: use --no-check-certificate in wget by default

A number of autobuilder failures are due to the fact that autobuilder
instances use old distributions, with old SSL certificates, and
therefore wget aborts with an error "The certificate of `xyz.org' is
not trusted.".

In order to avoid such failures that are not very interesting in the
context of the autobuilders, we pass --no-check-certificate to
wget. The integrity of the downloaded files is anyway verified by the
hashes, and this is only meant to be used in the context of
testing/CI, not in production.

Signed-off-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>
Signed-off-by: Arnout Vandecappelle (Essensium/Mind) <arnout@mind.be>