Good News!
After backup VM's I Try to force install of procps ("apt-get install procps" with "YES" at the question), debian do the jobs, then I restarted
./pve-upgrade-1.9-to-2.0
After about half an hour the update going to end without errors!
Then I execute:
- a reboot
- /pve-upgrade-1.9-to-2.0 --import (to import old config).
And all seems to work well!!!
I try a couple of reboots to be shure that grub do his job.
So thank you Udo for the precious hint, you save my day (a very LONG day)