Add OpenSSH client package to linux servicing images

[kiazhi]

PR Summary

1. Addresses Enhancement request: Add ssh to images #374 enhancement request for linux servicing images.

In order to use Enter-PSSession to connect with other (Windows or Linux) VM and Container, OpenSSH client package is required.

Below is the list of OpenSSH client package required for various linux distros:

• openssh-clients package for Centos
• openssh-client package for Debian
• openssh-clients package for openSUSE
• openssh-client package for Ubuntu

PR Checklist

• PR has a meaningful title
  • Use the present tense and imperative mood when describing your changes
• Summarized changes
• Change is not breaking
• Make sure all Dockerfile, .sh, .ps1 and .psm1 files have the correct copyright header
• This PR is ready to merge and is not Work in Progress.
  • If the PR is work in progress, please add the prefix WIP: to the beginning of the title and remove the prefix when the PR is ready.
• Adds a new image or tag
  • Not Applicable
• OR
  • Update README.powershellcommunity.md
  • Update vsts-ci.yml