201-confidential-os-disk patch (#141)

* add default value for variables; add random string for rgn

quickstart/201-confidential-os-disk/outputs.tf

@@ -0,0 +1,7 @@
+output "resource_group_name" {
+  value = azurerm_resource_group.example.name
+}
+
+output "managed_disk_name" {
+  value = azurerm_managed_disk.main.name
+}