jenkins/: Use tfgit.checkout_ci_scripts()

Consistently use single function for clone tf-m-ci-scripts repo with
parameters defined by job (e.g. specifying a change reference to fetch).

Signed-off-by: Paul Sokolovsky <paul.sokolovsky@linaro.org>
Change-Id: I76eb4c6c31633b98489f82d29015c7d9486418ff
8 files changed