Per cluster data-root doesn't sanatize cluster

[johrstrom]

I accidentally made this per-cluster dataroot which is obviously wrong.

data/batch_connect/["kubernetes", "kubernetes-test", "kubernetes-dev"]/usr/johrstrom/classroom-jupyter

Here's the config to replicate. It's when you define the cluster in the form, and it's actually misconfigured to be a static array (should actually be a select widget with those options).

form:
- cluster
attributes:
  cluster:
     - 'kubernetes'
     - 'kubernetes-test'
     - 'kubernetes-dev'

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