Retrieve git revision of the top-level git repository

If this is included as a submodule, we'd get the revision for this
repository instead of the parent one.

roles/base/tasks/rollback_protection.yml

@@ -11,7 +11,10 @@
 # configuration.
 
 # Define parameters associated with the source.
-- local_action: shell git rev-parse HEAD
+- local_action:
+    module: shell
+    _raw_params: git rev-parse HEAD
+    chdir: {{ playbook_dir }}
   register: git_revision_cmd
   run_once: true
   become: false