osutil/disks: fix name resolving of devices

osutil/disks/mockdisk.go

@@ -305,15 +305,36 @@ func MockPartitionDeviceNodeToDiskMapping(mockedDisks map[string]*MockDiskMappin
 }
 
 func resolveName(deviceName string) (string, error) {
-	corrected := path.Join(dirs.GlobalRootDir, deviceName)
-	if osutil.IsSymlink(corrected) {
-		resolved, err := filepath.EvalSymlinks(corrected)
-		if err != nil {
+	resolve := func(p string) (string, error) {
+		if !osutil.FileExists(p) {
+			return "", nil
+		}
+		if osutil.IsSymlink(p) {
+			resolved, err := filepath.EvalSymlinks(p)
+			if err != nil {
+				return "", err
+			}
+			return resolved, nil
+		}
+		return p, nil
+	}
+
+	if res, err := resolve(deviceName); err != nil {
+		return "", err
+	} else if res == "" {
+		// did not exist, try again but with corrected path
+		if res, err := resolve(path.Join(dirs.GlobalRootDir, deviceName)); err != nil {
 			return "", err
+		} else if res == "" {
+			// did not exist at all, meaning we assume it's the name of
+			// the device, not a path
+			return deviceName, nil
+		} else {
+			return strings.TrimPrefix(res, dirs.GlobalRootDir), nil
 		}
-		corrected = resolved
+	} else {
+		return res, nil
 	}
-	return strings.TrimPrefix(corrected, dirs.GlobalRootDir), nil
 }
 
 // MockDeviceNameToDiskMapping will mock DiskFromDeviceName such that the