set HOME variable when not available, e.g when running with cloud-init

[jsiebens]

Description

Apparently, HOME variable isn't always set when cloud-init executes a startup script, causing the install.sh script to fail. This PR adds an additional check to see if this is the case and sets the variable if required.

Motivation and Context

• [x] I have raised an issue to propose this change this is required fixes #282

How Has This Been Tested?

Launched multiple VMs, locally with lima or mulitpass and on different cloud providers (GPC and AWS using Terraform) with this updated install script.

Types of changes

• [x] Bug fix (non-breaking change which fixes an issue)
• [ ] New feature (non-breaking change which adds functionality)
• [ ] Breaking change (fix or feature that would cause existing functionality to change)

Checklist:

Commits:

• [x] I've read the CONTRIBUTION guide
• [ ] My commit message has a body and describe how this was tested and why it is required.
• [x] I have signed-off my commits with git commit -s for the Developer Certificate of Origin (DCO)

Code:

• [ ] My code follows the code style of this project.
• [ ] I have added tests to cover my changes.

Docs:

• [ ] My change requires a change to the documentation.
• [ ] I have updated the documentation accordingly.

[alexellis]

Thanks for this PR.