Set the connection method.

In renew-hosts, I'm using a local connection and delegation breaks. So
set it for the hosts (better than doing it for each delegated task).

hosts/all.yaml

@@ -17,6 +17,7 @@ all:
   vars:
     # Force usage of Python3.
     ansible_python_interpreter: python3
+    ansible_connection: ssh
   children:
     pkg_mgr_apt:
     pkg_mgr_opkg: