Don't recreate GCE instances when updating resource_policies property

[hanneshayashi]

This should fix the behaviour described in #9981.
Basically, the change removes the ForceNew attribute from the resource_policies property of google_compute_instance and adds code to check for changes of the property. If the property changed, all old values get removed and all new values (if there are any) get added.

[hanneshayashi]

Friendly ping @edwardmedia. I appreciate that you assigned #9981 to me, but unfortunately I can't approve my own PR 😃
Would you mind reviewing my changes? Thank you!

[nat-henderson]

This looks good to me, I will run the tests.

[hanneshayashi]

Looks like the test is failing on an unrelated file. Do you want me to rebase the branch with the current master?
Edit: Just for completeness sake, I did run "make fmt" and it did not produce any changes 🤷

[nat-henderson]

Hm, yeah, the linter is failing ... but that can't realistically be your fault, can it? Let's move to the next step. :)

This code is automatically generated by a tool called Magic Modules, which keeps this code in sync across ga, beta, and other occasional early access Terraform providers.

Fortunately, this file is pretty easy to edit in Magic Modules - it's here:

https://github.com/GoogleCloudPlatform/magic-modules/blob/master/mmv1/third_party/terraform/resources/resource_compute_instance.go.erb

You'll notice that it uses some erb features - to exclude things from ga, for instance - but that shouldn't impact your change. Can you move these changes to that file and open a new PR in Magic Modules, linking it to this PR?

[hanneshayashi]

I have created a new PR for Magic Modules: GoogleCloudPlatform/magic-modules#5206

[hanneshayashi]

Closing this, because this was merged into Magic Modules.

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