fvp|juno_utils.sh: several changes on yaml generation

This is a collection of changes required in order to produce correct
yaml files which ultimatelly are consumed by LAVA on behalf of
Open CI jobs [1]. Changes are done on top of [2], with the aim of
keeping [2] intact (the revert) and clearly identifying those required
changes while implementing & testing [1].

[1] https://review.trustedfirmware.org/c/ci/tf-a-job-configs/+/6217
[2] https://review.trustedfirmware.org/c/ci/tf-a-ci-scripts/+/6223

Signed-off-by: Leonardo Sandoval <leonardo.sandoval@linaro.org>
Change-Id: I8506416ef66ba283b336c82208ffc07bf0b2dc3b
5 files changed