nvme: enable specifying warnings and criticals for serial numbers

plugins/disk/nvme

@@ -24,6 +24,12 @@ name, e.g., 'nvme0n1', to make environment variable:
     env.nvme_usage_nvme0n1_warning 5:
     env.nvme_usage_warning 8:
 
+If your device names change on reboot you can also use the labels
+(based on serial numbers) to set the warning and critical labels
+
+    env.nvme_usage_SN_1234567_warning 8:101
+    env.nvme_usage_SN_1234567_critical 5:101
+
 =head1 INTERPRETATION
 
 This is a multigraph plugin which makes three graphs.
@@ -191,8 +197,10 @@ sub smart_log {
 sub my_print_thresholds {
     my ($label, $graph, $device, $warn_default, $crit_default) = @_;
     my $dev = basename($device);
-    my ($warn, $crit) = get_thresholds($graph, "${graph}_${dev}_warning", "${graph}_${dev}_critical",
+    my ($warn_label, $crit_label) = get_thresholds($graph, "${graph}_${label}_warning", "${graph}_${label}_critical",
                                        $warn_default, $crit_default);
+    my ($warn, $crit) = get_thresholds($graph, "${graph}_${dev}_warning", "${graph}_${dev}_critical",
+                                       $warn_label, $crit_label);
     print "${label}.warning $warn\n" if defined $warn;
     print "${label}.critical $crit\n" if defined $crit;
 }