Add OpenSSH to installed package

[philipmat]

This would allow reusable connections (-c ssh).

Might also need the sshpass package until this pull request is accepted.

[William-Yeh]

Similar to #14

At first, I designed these series of images according to the best practice of Docker: If you run SSHD in your Docker containers, you're doing it wrong! So I didn't try to touch any SSH stuff unless absolutely necessary.

So, I prefer installing such stuff at derived images or by another script (maybe install-openssh.sh?).

[philipmat]

Sorry if I wasn't clear. I'm not talking about the ssh daemon, but the ssh client libraries. This allows Ansible to use OpenSSH libraries over paramiko:

In Ansible 1.2.1 and later, ‘ssh’ will be used by default if OpenSSH is new enough to support ControlPersist as an option.
Paramiko is great for starting out, but the OpenSSH type offers many advanced options.

https://support.ansible.com/hc/en-us/articles/201957917-How-do-I-get-ansible-to-reuse-connections-enable-Kerberized-SSH-or-have-Ansible-pay-attention-to-my-local-SSH-config-file-

[William-Yeh]

Now openssh-client/clients and sshpass are installed on all images, excluding the images with -onbuild and mini- tags.