[lib][schema] Make kavlan hashes optional

This allows the schema to validate even when kavlan is set to false for a
cluster (such as when initially installing a cluster).
5 jobs for general_fixes in 4 minutes and 41 seconds (queued for 1 second)
Status Job ID Name Coverage
  Validate
passed #822551
grid5000-docker
rubocop

00:00:24

passed #822552
grid5000-docker
validate-data

00:01:05

 
  Generate
passed #822553
grid5000-docker
generate-reference-api

00:01:02

 
  Deploy
passed #822554
grid5000-shell
deploy

00:00:06

passed #822555
grid5000-docker
rspec

00:02:33