This:
- drops the previous version of the tooling
- installs the new tooling:
- use set -e in the main script (so failure are immediately detecting by icinga)
- the new scripts updates all instances at once (in working order, first opam root
with the default opam instance, then the other secondary repositories).
- The overall script triggered by the timer/service is looping other all instances to
init or update them all (in the proper order)
Related to T3826