This makes the OS disk type configurable for Azure deployments.

Also, this change sets the default OS disk type to Standard_LRS rather than StandardSSD_LRS (which seems to be the default in Azure), since a cheaper disk does not appear to come with any significant perfomance penalty in this case.

Description

• The type of disk to use for the VM OS is made configurable.
• The default disk type becomes a non-SSD one.

Motivation and Context

We can use a cheaper disk without performance penalty.

How Has This Been Tested?

By deploying to Azure cloud.

Types of changes

• 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 not work as expected)

Checklist:

• I have read the CONTRIBUTING document.
• My code follows the code style of this project.
• [] My change requires a change to the documentation.
• [] I have updated the documentation accordingly.
• [] I have added tests to cover my changes.
• [] All new and existing tests passed.