Add takeover based HUP script

[kb2ma]

This script is equivalent to upgrade-2.x.sh, but for takeover based HUP. This script is derived from upgrade-2.x.sh, but removes unnecessary functionality. It also aims to be a model for a script implementation but avoiding gratuitous changes to the upgrade-2.x.sh original.

I am looking for higher level comments on the approach at this point. I have added some questions in the code. Don't mind the individual commits. I will squash them later.

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[kb2ma]

@alexgg Fixed up from your review and rebased. All changes are in the final commit. In addition to your review, I did these things:

• Renamed "takeover_path" to "work_dir". It's more descriptive, especially since adding the cleanup function
• Added some options to the takeover binary to accommodate how it works now

If it looks OK, I'll squash down to a single commit for final approval.