diskmanage: improve setting usage for whole disk with include-partitions

in case a disk with partitions also has an fstype set, which happens for our ZFS
boot disks. Do not change the behavior without include-partitons, as we
prefer(red) to be more specific than simply 'partitions' then.

Reported in the enterprise support channel.

Signed-off-by: Fabian Ebner <f.ebner@proxmox.com>

PVE/Diskmanage.pm

@@ -713,6 +713,9 @@ sub get_disks {
 		next if $partitions->{$part}->{used} eq 'partition';
 		$used //= $partitions->{$part}->{used};
 	    }
+	} else {
+	    # fstype might be set even if there are partitions, but showing that is confusing
+	    $used = 'partitions' if scalar(keys %{$partitions});
 	}
 	$used //= 'partitions' if scalar(keys %{$partitions});
 	# multipath, software raid, etc.