jobs variable reset only works when upgrading format from 2.0 -> 2.2, not 2.0 -> 2.1 -> 2.2

[dra27]

When upgrading from a 2.0 root directly to 2.2, one gets:

[NOTE] The 'jobs' option was reset, its value was 255 and its new value will vary according to the current number of cores on your machine. You can restore the fixed
       value using:
           opam option jobs=255 --global

If the root has already been upgraded to 2.1, this check is skipped (and the old, fixed value, persists).

Not clear on the impact - it just probably just means a lot of users have a hard-coded wrong opam 2.1 value.

[rjbou]

linked to #5284