automation: edit pipeline to prevent running non-selected jobs

Filtering jobs using the selected jobs regex is missing for
qemu-export + yocto jobs when running regular pipelines and eclair jobs
when running scheduled pipelines.

First, set a default value for the selected jobs regex to remove the
need to always check if the variable is empty.

Then add the missing rules to filter out those jobs.

Signed-off-by: Victor Lira <victorm.lira@amd.com>
Reviewed-by: Stefano Stabellini <sstabellini@kernel.org>

.gitlab-ci.yml

@@ -2,6 +2,7 @@ variables:
   XEN_REGISTRY: registry.gitlab.com/xen-project/xen
   SELECTED_JOBS_ONLY:
     description: "Regex to select only some jobs, must be enclosed with /. For example /job1|job2/"
+    value: "/.*/"
 
 workflow:
   name: "$CI_PIPELINE_SCHEDULE_DESCRIPTION"