nixos/filesystems/zfs: Use proper script mode

Tell zpool-list(8) to format output rather than modifying it afterwards.

Furthermore, pool names may contain spaces and would thus break due to
awk(1)'s word splitting.

nixos/modules/tasks/filesystems/zfs.nix

@@ -666,7 +666,7 @@ in
           # expand every pool. Otherwise we want to enumerate
           # just the specifically provided list of pools.
           poolListProvider = if cfgExpandOnBoot == "all"
-            then "$(zpool list -H | awk '{print $1}')"
+            then "$(zpool list -H -o name)"
             else lib.escapeShellArgs cfgExpandOnBoot;
         in
         {