Add Ubuntu LIS setup to ProvisionLinuxForLisa script

Also fixes following issues in ProvisionSshKeys.ps1 script:
- plink should now be able to run and get distro
- Alternative to systemctl commands (which are not available in Ubuntu
14.04 and below)
- append public keys to authorized_keys; instead of overwriting
Merge remote-tracking branch 'upstream/master'
Merge pull request #88 from alexngmsft/master

Add Ubuntu LIS component installation to provisioning script for LISA