automation: use expect to run QEMU

automation: use expect to run QEMU

Use expect to invoke QEMU so that we can terminate the test as soon as
we get the right string in the output instead of waiting until the
final timeout.

For timeout, instead of an hardcoding the value, use a Gitlab CI
variable "QEMU_TIMEOUT" that can be changed depending on the latest
status of the Gitlab CI runners.

Signed-off-by: Stefano Stabellini <stefano.stabellini@amd.com>
Reviewed-by: Michal Orzel <michal.orzel@amd.com>