Prevent recreation of compute_instance_template on every apply

[madmod]

The device_name was always empty so I explicitly set it to the computed value to prevent Terraform recreating it on each apply. This might be a bug in the Google provider, but I haven't found an issue for it yet.

[josh-padnick]

@madmod Thanks for submitting this PR! I didn't experience the google_compute_instance_template being recreated on each terraform apply unless I made a change that would trigger such a change. Are you saying even unrelated changes trigger a destroy/re-create and that adding the device-name property as specified in this PR fixed it?

If so, that sounds like buggy behavior to me and we should report on the Google Terraform GitHub repo.

[josh-padnick]

@madmod I finally tried to recreate this issue, and I couldn't, although I did find other issues which I resolved in #4. When I terraform apply the root example, it works fine. When I run another terraform plan or terraform apply there are no subsequent changes. Are you applying a different example, or following a different workflow?

[josh-padnick]

Closing this PR due to inactivity, but happy to reconsider it if needed.