fuse integration: normalize config in Setup and clean the work dir too

Setup(nil) panicked on config.EnableDebug and external-mount Cleanup left
the temp dir behind; use the stored config for the start* calls and remove
tempDir alongside the external work dir.

Generated with [Devin](https://devin.ai)

Co-Authored-By: Devin <158243242+devin-ai-integration[bot]@users.noreply.github.com>

test/fuse_integration/framework_test.go

@@ -137,6 +137,7 @@ func (f *FuseTestFramework) Setup(config *TestConfig) error {
 	if config != nil {
 		f.config = config
 	}
+	config = f.config
 
 	dirs := []string{f.mountPoint, f.logDir, f.dataDir}
 	for _, dir := range dirs {