Add make iso-menuconfig, avoid host-tar build for linux-menuconfig

Makefile

@@ -142,11 +142,17 @@ minikube_iso: # old target kept for making tests happy
 	$(MAKE) -C $(BUILD_DIR)/buildroot
 	mv $(BUILD_DIR)/buildroot/output/images/rootfs.iso9660 $(BUILD_DIR)/minikube.iso
 
+# Change buildroot configuration for the minikube ISO
+.PHONY: iso-menuconfig
+iso-menuconfig:
+	$(MAKE) -C $(BUILD_DIR)/buildroot menuconfig
+	$(MAKE) -C $(BUILD_DIR)/buildroot savedefconfig
+
 # Change the kernel configuration for the minikube ISO
 .PHONY: linux-menuconfig
 linux-menuconfig:
-	$(MAKE) -C $(BUILD_DIR)/buildroot linux-menuconfig
-	$(MAKE) -C $(BUILD_DIR)/buildroot linux-savedefconfig
+	$(MAKE) -C $(BUILD_DIR)/buildroot/output/build/linux-$(KERNEL_VERSION)/ menuconfig
+	$(MAKE) -C $(BUILD_DIR)/buildroot/output/build/linux-$(KERNEL_VERSION)/ savedefconfig
 	cp $(BUILD_DIR)/buildroot/output/build/linux-$(KERNEL_VERSION)/defconfig deploy/iso/minikube-iso/board/coreos/minikube/linux_defconfig
 
 out/minikube.iso: $(shell find deploy/iso/minikube-iso -type f)