add diskspace to isobuilder1-4

the isobuilders are running low on diskspace and i can’t see any non-essentials eating up significant amounts of diskspace, so i’m tempted to give them all 1gb extra on vg1-root, what do you think?

Related issues

Related to #13425 (closed)
Blocks #13233 (closed)

Original created by @groente on 14732 (Redmine)

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