add a linux VM as a jumpbox to Bastion SSH into the Hub network

[glennmusa]

Description

Adds a Linux virtual machine that defaults to Ubuntu 18.04 LTS to use as a jumpbox from a Bastion host in the Hub network.

Issue reference

The issue this PR will close: #188

Checklist

Please make sure you've completed the relevant tasks for this PR, out of the following list:

• Code compiles or validates correctly
• BASH scripts have been validated using shellcheck
• All tests pass (manual and automated)
• The documentation is updated to cover any new or changed features
• Markdown files have been linted using the recommended linter. (See .vscode/extensions.json.)
• Relevant issues are linked to this PR

[brooke-hamilton]

@glennmusa Just a question: why do the names of the Bastion instance and the VMs (and related resources) have a default prefix of "mlzDemo"? Is it because we expect users to modify the Bastion and jump box resources before using them?

[glennmusa]

@glennmusa Just a question: why do the names of the Bastion instance and the VMs (and related resources) have a default prefix of "mlzDemo"? Is it because we expect users to modify the Bastion and jump box resources before using them?

@brooke-hamilton I don't think there was ever consensus or intentional design around default .tfvars values. "mlzDemo" seems to have emerged as a naming convention.

I want to say that for the most part the Terraform in the solution has treated most configurable settings as input via Terraform .tfvars files, but I don't see why there isn't a future where the configuration(s) could be made up of calculated values: A) the input via .tfvars files with B) calculated values that include environment variables like mlz_env_name.