Ignore partitions on NVME devices by default

The convention of the linux driver is nvme($device)n($namespace)p($partition). On *bsd it seems to be different, using "ns" instead of "n" as the namespace separator.

collector/diskstats_linux.go

@@ -35,7 +35,7 @@ const (
 )
 
 var (
-	ignoredDevices = flag.String("collector.diskstats.ignored-devices", "^(ram|loop|fd|(h|s|v|xv)d[a-z])\\d+$", "Regexp of devices to ignore for diskstats.")
+	ignoredDevices = flag.String("collector.diskstats.ignored-devices", "^(ram|loop|fd|(h|s|v|xv)d[a-z]|nvme\\d+n\\d+p)\\d+$", "Regexp of devices to ignore for diskstats.")
 )
 
 type diskstatsCollector struct {