Multi Node/Context support for mirroring Git workspaces via kubectl

The mirroring of git workspaces to k8s pod nodes is done by piping a git
push command through `kubectl exec`. Without specifying a k8s context
for kubectl, the `current-context` from the kubeconfig is used. This is
problematic in multi-node scenarios where different nodes reside in
different namespaces and thus, are reachable via separate contexts.
Ansible cannot handle the context switch automatically as it would via
the inventory and its kubectl connection plugin because we are running
the git push from the executor/localhost.
This change makes sure the correct context of the corresponding node is
passed to `kubectl exec` explicitly, thus pushing the git repos to the
correct k8s pod.

Change-Id: Ic0b11b5860bb0062b3a1c068f4f963fb76018715

roles/mirror-workspace-git-repos/tasks/main.yaml

@@ -11,7 +11,7 @@
 - name: Synchronize src repos to workspace directory
   command: |-
     {% if ansible_connection == "kubectl" %}
-      git push {% if mirror_workspace_quiet %}--quiet{% endif %} --mirror "ext::kubectl -n {{ zuul.resources[inventory_hostname].namespace }} exec -i {{ zuul.resources[inventory_hostname].pod }} -- %S {{ ansible_user_dir }}/{{ zj_project.value.src_dir }}"
+      git push {% if mirror_workspace_quiet %}--quiet{% endif %} --mirror "ext::kubectl --context {{ zuul.resources[inventory_hostname].context }} -n {{ zuul.resources[inventory_hostname].namespace }} exec -i {{ zuul.resources[inventory_hostname].pod }} -- %S {{ ansible_user_dir }}/{{ zj_project.value.src_dir }}"
     {% else %}
       git push {% if mirror_workspace_quiet %}--quiet{% endif %} --mirror git+ssh://{{ ansible_user }}@{{ ansible_host | ipwrap }}:{{ ansible_port }}/{{ ansible_user_dir }}/{{ zj_project.value.src_dir }}
     {% endif %}