This reverts merge request !26991

Bump the helm and kubectl used in our Kubernetes integration, used e.g.
to install apps.

Note I have only bumped to the latest patch of the v1.11 series for
kubectl as GKE clusters are still on 1.10/1.11

Signed-off-by: Takuya Noguchi <takninnovationresearch@gmail.com>

Enables frozen string for the following:

* lib/gitlab/hook_data/**/*.rb
* lib/gitlab/i18n/**/*.rb
* lib/gitlab/import/**/*.rb
* lib/gitlab/import_export/**/*.rb
* lib/gitlab/kubernetes/**/*.rb
* lib/gitlab/legacy_github_import/**/*.rb
* lib/gitlab/manifest_import/**/*.rb
* lib/gitlab/metrics/**/*.rb
* lib/gitlab/middleware/**/*.rb

Partially addresses gitlab-org/gitlab-ce#47424.

This will reduce dependencies and failure points during installation. It
will also reduce security risks from untrusted dependencies being able
to effect all our users

Ensure `Namespace`'s is namespaced in `Gitlab::Kubernetes::Helm#initialize` and fix a transient failing spec due to that

Signed-off-by: Rémy Coutable <remy@rymai.me>