.gitlab-ci.yml: Restore building most of our jobs

.gitlab-ci.yml: Restore building most of our jobs

We are changing the primary build jobs to use "when"
not "only".  These a similar and related GitLab syntax
tools to control when jobs are run.

With 'when' now in use it must be specified on all jobs
that inherit from each other via:

.extends .shared_template

"only" can be left however for the pages and coverity as
these use:

.extends .shared_runner_build_image

BUG: https://bugzilla.samba.org/show_bug.cgi?id=14861

Signed-off-by: Andrew Bartlett <abartlet@samba.org>
Reviewed-by: Douglas Bagnall <douglas.bagnall@catalyst.net.nz>