ewaol-distro: Validate Required Containers Kernel config

Added task containers_kernelcfg_check to validate that the kernel config
required for running containers is present in final kernel configuration.

Using docker.cfg from yocto-kernel-cache as required list.

Issue-Id: SCM-2356
Signed-off-by: Nathan Dunne <Nathan.Dunne@arm.com>
Signed-off-by: Diego Sueiro <diego.sueiro@arm.com>
Change-Id: I3f50d9ef05483695817dded83e6f5c479db5ed41