Prior to this commit, this exposed a virtualenv stats.export.s.o which is no
longer accessible (from munin0 node). Simplifying this to export the rrd file
in the munin(0)'s apache venv and expose it through the existing
stats.export.s.o host's front (pergamon).

This diff allows to:

• remove the obsolete stats.export.s.o virtualenv from munin0 (unused)
• expose the export history_counters.json directly from munin0 http://munin.internal.s.o/export/history_counters.json
• update pergamon's role to actually answer correctly requests from https://stats.export.s.o/ (proxying requests to http://munin.internal.s.o/export/)

There remains work to renew the certificate use for the fqdn
stats.export.s.o but that's not in the scope of the diff.

Related T1544

bin/octocatalog pergamon ~> wants to:

• install a virtualenv stats.export.s.o
• with proxy requests to munin.internal.s.o

bin/octocatalog munin ~> wants to:

• remove apache configuration about stats.export.s.o virtualenv
• add the rewrite rule to export folder in munin virtualenv
• update the crontab entry to actually write to the right location the history_counters.json