Setting tag sfa-3.1-10

rewrote an optimized version of verify_persons in the PL driver:
Allocate and Provision should now perform much faster
in the bargain, changed the way dummy persons are created by SFA:
the sfa email is used when free, otherwise a fake email is made up from hrn
e.g. hrn=onelab.inria.thierry_parmentelat -> email=thierry_parmentelat@onelab.inria.stub
verify_chain debug flow does not up any more by default
various fixes in the iotlab driver