Makefile: ensure repo is clean before testing

.travis.yml

@@ -20,6 +20,7 @@ install: true
 
 script:
   - make
+  - make clean
   - make unit
   - make lint
   - make container

Makefile

@@ -267,10 +267,10 @@ push-name:
 	@echo "pushed: $(IMAGE):$(ARCH)-$(VERSION)"
 
 clean: container-clean bin-clean
-	rm -r .cache
+	rm -rf .cache
 
 container-clean:
-	rm -rf .container-* .push-*
+	rm -rf .container-* .manifest-* .push-*
 
 bin-clean:
 	rm -rf bin