Merged 1.21 upgrade steps into one list

Without this, upgrade steps really end up running in the wrong
order. Steps like the machine and instanceData env UUID migrations
really need to go first.

This change solves the immediate issue. A future change will tidy
this up so that the steps can be assigned against 1.21 final instead
of alpha1.
Merge pull request #1008 from mjs/merge-121-upgrade-steps

Merged 1.21 upgrade steps into one list

Without this, upgrade steps really end up running in the wrong order. Steps like the machine and instanceData env UUID migrations really need to go first.

This change solves the immediate issue. A future change will tidy this up so that the steps can be assigned against 1.21 final instead of alpha1.