Acceptance tests: add Linux initrd checking test

Acceptance tests: add Linux initrd checking test

QEMU used to exits with a not accurate error message when
an initrd > 2GiB was passed. That was fixed on patch:

	commit f3839fda5771596152b75dd1e1a6d050e6e6e380
	Author: Li Zhijian <lizhijian@cn.fujitsu.com>
	Date:   Thu Sep 13 18:07:13 2018 +0800

    	change get_image_size return type to int64_t

This change adds a regression test for that fix. It starts
QEMU with a 2GiB dummy initrd, and checks that it evaluates the
file size correctly and prints an accurate message.

Signed-off-by: Wainer dos Santos Moschetta <wainersm@redhat.com>
Reviewed-by: Caio Carrara <ccarrara@redhat.com>
Reviewed-by: Cleber Rosa <crosa@redhat.com>
Reviewed-by: Eduardo Habkost <ehabkost@redhat.com>
Reviewed-by: Philippe Mathieu-Daudé <philmd@redhat.com>
Tested-by: Philippe Mathieu-Daudé <philmd@redhat.com>
Message-Id: <20181109182153.5390-1-wainersm@redhat.com>
Signed-off-by: Eduardo Habkost <ehabkost@redhat.com>