[ImageExport] allow custom compute service account

[dntczdx]

No description provided.

[google-oss-robot]

Skipping CI for Draft Pull Request.
If you want CI signal for your change, please convert it to an actual PR.
You can still manually trigger a test run with /test all

[zoran15]

Suggested change

	flagSet.Var((*flags.TrimmedString)(&args.ComputeServiceAccount), "compute_service_account",
	"Compute service account to override default.")
	flagSet.Var((*flags.TrimmedString)(&args.ComputeServiceAccount), "compute_service_account",
	"Compute service account to be used by exporter Virtual Machine.")

[dntczdx]

let me remove it for now since I only work on export...

[EricEdens]

Based on the directory of this file, I'm assuming you'll want to re-use the accounts in other test suites. To help clarify your intent, I'd suggest the following changes:

1. Rename the file to accounts.go or projects.go
2. Create well-named methods that return a struct (as described below). Eg: ProjectWithDefaultServiceAccount() project

[dntczdx]

I want to reuse cross test suites, yes. Also, there are more variables to add for rich test scenarios. So I keep variables.go to contain all additional test variables parsing for test suites.

[google-oss-robot]

[APPROVALNOTIFIER] This PR is APPROVED

This pull-request has been approved by: dntczdx, EricEdens, zoran15

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