Remove error wrapper from /sys/class/power_supply (#308)

SuperQ · web-flow · commit 4486fb2353fd · 2020-06-14T08:40:17.000+02:00
Don't wrap the error of `ioutil.ReadDir()` so that the error return can
be tested with `os.IsNotExist()`. Fixes node_exporter log noise.

```
caller=collector.go:161 msg="collector failed" name=powersupplyclass duration_seconds=0.00079848 err="could not get power_supply class info: error obtaining power_supply class info: failed to list power supplies at \"/sys/class/power_supply\": open /sys/class/power_supply: no such file or directory"
```

Signed-off-by: Ben Kochie &lt;superq@gmail.com&gt;
diff --git a/sysfs/class_power_supply.go b/sysfs/class_power_supply.go
@@ -110,7 +110,7 @@ func (fs FS) PowerSupplyClass() (PowerSupplyClass, error) {
 
 	dirs, err := ioutil.ReadDir(path)
 	if err != nil {
-		return nil, fmt.Errorf("failed to list power supplies at %q: %v", path, err)
+		return nil, err
 	}
 
 	psc := make(PowerSupplyClass, len(dirs))

Original file line number	Diff line number	Diff line change
`@@ -110,7 +110,7 @@ func (fs FS) PowerSupplyClass() (PowerSupplyClass, error) {`
`110`	`110`
`111`	`111`	`dirs, err := ioutil.ReadDir(path)`
`112`	`112`	`if err != nil {`
`113`		`- return nil, fmt.Errorf("failed to list power supplies at %q: %v", path, err)`
	`113`	`+ return nil, err`
`114`	`114`	`}`
`115`	`115`
`116`	`116`	`psc := make(PowerSupplyClass, len(dirs))`