Kas supports 'reference repositories' which are used as a local source
of git objects to speed up fetches. At the beginning of the CI run we
can update these repositories once to speed up later fetches.
Change-Id: I138051fd3cf9b5675e0fa5007cd8088abd17db4e
Signed-off-by: Ross Burton <ross.burton@arm.com>
Signed-off-by: Jon Mason <jon.mason@arm.com>