oeqa: Use snapshot instead of copying the rootfs image
Rather than copying images, use the snapshot option to qemu. This fixes a regression
caused by the recent runqemu changes where the wrong images were being testes since
the image is copied without the qemuboot.conf file. This means the latest image is
found by runqemu rather than the specified one, leading to various confused testing
results.
It could be fixed by copying more files but use snapshot mode instead.
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>
