[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 schema_kavlan_optional in 4 minutes and 32 seconds (queued for 1 second)
latest
Status Job ID Name Coverage
  Validate
passed #820180
grid5000-docker
rubocop

00:00:24

passed #820181
grid5000-docker
validate-data

00:01:05

 
  Generate
passed #820182
grid5000-docker
generate-reference-api

00:01:00

 
  Deploy
passed #820183
grid5000-shell
deploy

00:00:04

passed #820184
grid5000-docker
rspec

00:02:25