Add SSH provider

[smarlowucf]

There are cases where it would be helpful to run IPA tests against an instance via SSH without the requirement of provider credentials.

• The SSH backend would require a new instance-ip argument.
• All methods that require API authentication will do nothing (pass).
• A new flag will be required --ssh-only and provider will still be a required argument.

ipa test ... --instance-ip 10.0.0.1 --ssh-only ec2

If the repos test can pull CSP name from metadata it could be updated and this would then just be a new provider name. #112

ipa test ... --instance-ip 10.0.0.1 ssh