Setting tag sfa-3.1-15

Setting tag sfa-3.1-15
major rework of the iotlab driver, that uses an IoT-lab REST API
and so does not need to interact with LDAP and OAR directly
deprecated cortexlab driver altogether
cosmetic changes in displaying credentials, rights and certificates
for hopefully more readable error messages
always start postgresql if not running (ignore /etc/myplc-release)
does not need lxc=enter-namespace anymore for make sync