Have the incremental upgrade process use less RAM

Originally created by @intrigeri on #6876 (Redmine)

As part of this work, we should update some hardcoded constants:

• memory_needed and space_needed in Tails::IUK::Frontend (the very goal of this work is to decrease these values)
• MIN_AVAILABLE_MEMORY in config/chroot_local-includes/usr/local/bin/tails-upgrade-frontend-wrapper (since #17152 (closed) was done, likely the Upgrader can work with less free memory)

Feature Branch: feature/15281-single-squashfs-diff, iuk:feature/11131-endless-upgrade, iuk:feature/15281-single-squashfs-diff

Attachments

• 2017Q3.stats
• 2018Q1.stats
• 2017Q4.stats
• 2018Q2.stats
• 2018Q3.stats

Parent Task: #15283 (closed)

Subtasks

• #17152 (closed)

Related issues

• Related to #6877 (closed)
• Related to #10115 (closed)
• Related to #9373 (closed)
• Related to #8415 (closed)
• Related to #15955 (closed)
• Related to #16015 (closed)
• Related to #5502