virttest.qemu_vm: set global_image_bootindex to 1 when using -kernel

As -kernel option should take the bootindex 0, so we should make
global_image_bootindex for images bootindex count start from 1.

Signed-off-by: Yiqiao Pu <ypu@redhat.com>
guest-os: Change kickstart/unattended parameters passed to kernel

With recent changes in the QEMU VM code, the cdrom order
is not honored anymore. Let's change the linux guests
configuration to honor that change.

Signed-off-by: Lucas Meneghel Rodrigues <lmr@redhat.com>