add CI_REFSPEC parameter to various jobs

The patch adds CI_REFSPEC parameter to the following
jobs to enable testing a specific tf-a-ci-scripts refspec.

- tf-daily
- tf-main
- tf-ci-gateway
- tf-coverity
- tf-static-checks

The patch also renames SCRIPTS_REFSPEC and SCRIPTS_PROJECT
variables in the clone script.

Signed-off-by: Zelalem Aweke <zelalem.aweke@arm.com>
Change-Id: I0b7b78b8b7c0d1bb7df81a37769978f366e83da0
6 files changed