tremplin: log full string when download parsing fails

Currently we just log the number that failed to parse, but it would also
be useful to have the full string.

BUG=b:282889041
TEST=deploy tremplin and install Crostini

Change-Id: Idfae32ce3db55e9fc75076108dc6fcc775258739
Reviewed-on: https://chromium-review.googlesource.com/c/chromiumos/platform/tremplin/+/4792134
Reviewed-by: Joel Hockey <joelhockey@chromium.org>
Commit-Queue: Daniel Verkamp <dverkamp@chromium.org>
Tested-by: Daniel Verkamp <dverkamp@chromium.org>
diff --git a/src/chromiumos/tremplin/tremplin.go b/src/chromiumos/tremplin/tremplin.go
index 572d9ea..7c3afc4 100644
--- a/src/chromiumos/tremplin/tremplin.go
+++ b/src/chromiumos/tremplin/tremplin.go
@@ -99,7 +99,7 @@
 
 	downloadPercent, err := strconv.ParseInt(matches[2], 10, 32)
 	if err != nil {
-		return 0, fmt.Errorf("failed to convert download percent to int: %q", matches[2])
+		return 0, fmt.Errorf("failed to convert download percent in '%q' to int: %q", progress, matches[2])
 	}
 
 	// Count metadata download as 0% of the total, since the entire rootfs still