[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).

lib/refrepo/valid/input/schemas/schema-node.yaml

@@ -23,11 +23,13 @@ chassis:
 exotic: optional_boolean
 gpu_devices: optional_hash
 kavlan:
-  <multi>:
-    <multi>: ip_address
+  <optional_hash>:
+    <multi>:
+      <multi>: ip_address
 kavlan6:
-  <multi>:
-    <multi>: ip_address
+  <optional_hash>:
+    <multi>:
+      <multi>: ip_address
 main_memory:
   ram_size: integer
   pmem_size: optional_integer