Add Compute Gallery images support

[puhley]

Summary of the Pull Request

The documentation for using custom images while fuzzing states that Compute Gallery images are supported. However, the existing code for handling custom images does not properly address Compute Gallery resource IDs. The code only handles references to Azure Images. This pull request adds support for Compute Gallery resource IDs as discussed in issue #1443 . In addition, it corrects an error within the existing code where an attempt to retrieve a "name" parameter is performed on the image "os_type". The "os_type" is a string and does not have a "name" parameter. This pull request removes the invalid "name" reference and converts the string using ".lower()" similar to the default code path.

PR Checklist

• Applies to work item: Incorrect handling of custom images #1443
• CLA signed. If not, go over here and sign the CLI.
• Tests added/passed
• Requires documentation to be updated
• I've discussed this with core contributors already. If not checked, I'm ready to accept this work might be rejected in favor of a different grand plan. Issue number where discussion took place: Incorrect handling of custom images #1443

Info on Pull Request

This pull request includes a check to determine whether the resource ID refers to a "galleries" resource type. If the resource ID is confirmed to be a Compute Gallery reference, then it will use the corresponding ComputeManagementClient methods and properties to retrieve the OS type. If an Azure Image reference is provided, then the code has been changed to provide the lower case value of the OS type. Since it was unknown what existing dependencies relied on the previous behavior, the code defaults to the existing approach of assuming an Azure Image reference was given.

Validation Steps Performed

This was tested locally within what is assumed to be a simple deployment environment. More robust testing is welcomed.

[ranweiler]

Thanks for this, @puhley. I have some small suggested changes, and a few comments, but the latter are more for us to follow up with.

[ranweiler]

Running integration tests.

[Porges]

@puhley out of interest, what type (distro/version) of Linux images are you deploying? We might need to make our agent binary "less portable" in order to comply with some security policies, so I'm trying to gather information on what distros are currently in use.