Enable ext4 image and disable wic in case of agl-container-guest-demo

Enable ext4 image and disable wic in case of agl-container-guest-demo

In case of AGL IC container integration, this method use
ext4 file system image to create guest rootfs.  It's reusing
wic tools.  In this case, the root filesystem for
container guest must be create  ext4 image.
On the other hand, the wic image build cause long build time.
It does not need in guest image build.

This patch fource enable ext4 image and  fource remove wic at
rootfs image build time.  It's aim to avoid hand operation by
each developer and reduce build time in guest image build.

Bug-AGL: SPEC-4766

Change-Id: I8ede8aecb489567a375f2842ed0942ebfa8cacd3
Signed-off-by: Naoto Yamaguchi <naoto.yamaguchi@aisin.co.jp>