workaround the unpacking hang issue (#245)

Author: inorthtyphoon

builder/context.go

@@ -102,7 +102,9 @@ func (b *Builder) scrapeDependencies(ctx context.Context, volName string, stepWo
 		scannerImageName,
 		"scan",
 		"-f", dockerfile,
-		"--destination", outputDir,
+		// NOTE (bindu): unpacking a tar file including .git folder can hang if --destination is a relative path
+		// Use the absolute path to workaround the issue.
+		"--destination", path.Join(normalizeWorkDir(stepWorkDir), outputDir),
 		context,
 	}