qemu.generic.cfg.unattended_install: Increase the install_timeout to 7200s for setting_cluster_size

Signed-off-by: Feng Yang <fyang@redhat.com>
qemu.generic: Add 128g_image_512_cluster_size sub unattended_install case.

Signed-off-by: Feng Yang <fyang@redhat.com>
Merge pull request #238 from FengYang/install

Install