According to `BootInterface` [1], the `prepare_ramdisk` method must
receive 3 arguments (self, task, ramdisk_params) while `FakeBoot`
implementation receives only 2 arguments (self, task).
This cause a runtime error when one wants one to use `FakeBoot` driver
as a part of its own driver (for test purposes or in case of standalone
Ironic with static PXE configuration).
The reason why it works now is, no one use `FakeBoot` without other fake
parts, so `prepare_ramdisk` is never called.
[1]: http://git.openstack.org/cgit/openstack/ironic/tree/ironic/drivers/base.py#n416
Change-Id: I0a55bfaf8aa58747ad2cfcd14ec84430d139e68c
6c1aa56429