Update makesystem for usig of fuel-ostf-tests repo

config.mk:
* Change using of OSTF repos to FUEL_OSTF_REPO
* Change usgae of Plugin and tests sha to FUEL_OSTF_COMMIT origin/master

repos.mk:
* Change build repo to build fuel-ostf repo from one repo

packages/eggs.module.mk:
* Change eval func to build fuel_ostf egg from fuel-ostf repo

Change-Id: I295de3feb5eff339a4c4d39dbbee1718a4d07c8a
Fixes: OSTF-237