Add initial support for automated frontend allocation for ERP5 SR.

Add initial support for automated frontend allocation for ERP5 SR.

Parameters are not final yet, and must evolve to get something resilient to
frontend "movements" (ex: frontend machine dying and frontend being
re-allocated on another, or frontend being replaced by an instance from
another software release - as it will happen for upgrades).

Modifed from original version by Rafael in order to fix conflicts
on md5 of the files and changes on same file done in multiple branches.