Revert "Access jenkins-tools.git using SSH (sysadmin#17729)"

This reverts commit b7905976.

The `jenkins-tools` repository is cloned as system user `jenkins`, which
doesn't have keys configured to access GitLab (only user has). I'll
revert this change and flag about this in the issue.

manifests/tester/check_po.pp

@@ -2,7 +2,7 @@
 class tails::tester::check_po (
   String $tools_repo_local_user             = 'jenkins',
   Stdlib::Absolutepath $tools_repo_checkout = '/var/lib/jenkins/tools',
-  String $tools_repo_url                    = 'git@gitlab-ssh.tails.boum.org:tails/jenkins-tools.git',
+  String $tools_repo_url                    = 'https://gitlab.tails.boum.org/tails/jenkins-tools.git',
   String $tools_repo_rev                    = 'master',
   String $tools_repo_ensure                 = 'latest',
 ) {