Retries ssh connection for Gather node certs (#10515)

This allows this task to work with a forks count > 10 and the default
configuration of sshd, which is to limit sessions to 10. (see
MaxSessions in sshd_config).

Since this is a delegate_to task, it connects to the same host (first
etcd) for each node in the cluster, thus easily going above 10.

Raising the ssh connection attempts allow for more robustness, without
decreasing the forks count or serialising the tasks, which could slow
the task (or the playbook as a whole, if decreasing forks).