Add support for optional images

Add support to allow optional image files in the BMC tarball.
This can be used for example to add a host bios file in a "System"
image, or for elements that as best practice should not be
updated unless necessary like for a bug fix, such as the U-Boot SPL.

This commit provides the ability to add these optional images from
a list of pre-defined names. These files will then go through the
same checks as the default image files such as checking the files
exist and the signature verification (if enabled) passes.

Change-Id: I304b4e28c776db4a51537613888b4e11824cab88
Signed-off-by: Adriana Kobylak <anoo@us.ibm.com>
5 files changed