logilab-common #10251578 Make the documentation reproducible [done]

Whilst working on the Reproducible Builds effort I noticed that logilab-common could not be built reproducibly. This is because the documentation embeds build-time non-deterministic variables via default keyword arguments. This patch uses the "foo=None / if foo is None" idiom.

priorityminor
typeenhancement
done in<not specified>
load left0.000
closed by<not specified>