Allow zpool configuration to be undefined for specific nodes

This does not impact existing nodes with the configuration already set (be it manually
or through puppet).

This will allow to configure storage1.staging as a rancher agent.

Refs. swh/infra/sysadm-environment#5164

data/hostname/storage1.internal.staging.swh.network.yaml

@@ -79,3 +79,4 @@ swh::deploy::storage::backend::workers: 40
 swh::deploy::storage::backend::max_requests: 5000
 swh::deploy::storage::backend::max_requests_jitter: 500
 
+zfs::common::zpool_configuration: {}

site-modules/profile/manifests/zfs/common.pp

 class profile::zfs::common {
-  $zpool_configuration = lookup('zfs::common::zpool_configuration')
+  # Allow zpool configuration to be undefined (that allows to bypass the manual
+  # configuration on some nodes e.g. storage1.staging)
+  $zpool_configuration = lookup('zfs::common::zpool_configuration', {default_value => {}})
 
-  # zpool create -f data /dev/vdb
-  zpool { 'data':
-    ensure => 'present',
-    *      => $zpool_configuration,
+  if $zpool_configuration {
+    # When provided, let's create the pool of data out of it
+    # zpool create -f data /dev/vdb
+    zpool { 'data':
+      ensure => 'present',
+      *      => $zpool_configuration,
+    }
+  } else {  # Otherwise, do nothing but ensure it's already configured
+    zpool { 'data':
+      ensure => 'present',
+    }
   }
 }