Before this patch, tobiko could customize provided guest images, such as
ubuntu images. This has been problematic recently, especially since
tobiko is executed on pods, because there have been issues to run
virt-customize with tobiko.
With this patch, tobiko tests expect an already customized guest image
included in its tobiko.conf.
If the tobiko ansible roles are used, by default they download an ubuntu
image and customize it, before executing tobiko tests.
Some parameter have been deprecated from tobiko.conf (python level),
such as `interface_name` and `customized_image_provided`.
Note: `interface_name` is still a valid ansible parameter because
ansible roles still customize ubuntu images.
Change-Id: Icde5fa5951dde79fec94a1c47366cc018785b1ed
b2103cbec9