Allow customizing the ROOTFS_DIR and CPIO_FILE variables

Author: gsingh93

Makefile

@@ -241,9 +241,9 @@ tools-vm_clean:
 ROOTFS_PARENT_DIR := $(ROOT_DIR)/rootfs
 ROOTFS ?= $(ROOTFS_PARENT_DIR)/rootfs-$(ARCH).img
 ROOTFS_FORMAT ?= qcow2
-ROOTFS_DIR := $(ROOTFS_PARENT_DIR)/alpine-$(ARCH)
+ROOTFS_DIR ?= $(ROOTFS_PARENT_DIR)/alpine-$(ARCH)
 INITRAMFS_DIR ?= $(ROOTFS_DIR)
-CPIO_FILE := $(ROOTFS_PARENT_DIR)/$$(basename $(INITRAMFS_DIR)).cpio.gz
+CPIO_FILE ?= $(ROOTFS_PARENT_DIR)/$$(basename $(INITRAMFS_DIR)).cpio.gz
 EXT4_SIZE ?= 1G
 
 $(ROOTFS_DIR):