r/compute_instance_template: Make disk.device_name computed

[radeksimko]

This is to address a breaking API change which occurred between yesterday and today. Last night's tests passed, but are now failing.

Test results (after patch)

=== RUN   TestAccComputeInstanceTemplate_importBasic
--- PASS: TestAccComputeInstanceTemplate_importBasic (26.45s)
=== RUN   TestAccComputeInstanceTemplate_importIp
--- PASS: TestAccComputeInstanceTemplate_importIp (47.83s)
=== RUN   TestAccComputeInstanceTemplate_importDisks
--- PASS: TestAccComputeInstanceTemplate_importDisks (27.77s)
=== RUN   TestAccComputeInstanceTemplate_importSubnetAuto
--- PASS: TestAccComputeInstanceTemplate_importSubnetAuto (107.90s)
=== RUN   TestAccComputeInstanceTemplate_importSubnetCustom
--- PASS: TestAccComputeInstanceTemplate_importSubnetCustom (90.38s)
=== RUN   TestAccComputeInstanceTemplate_basic
--- PASS: TestAccComputeInstanceTemplate_basic (24.88s)
=== RUN   TestAccComputeInstanceTemplate_preemptible
--- PASS: TestAccComputeInstanceTemplate_preemptible (25.28s)
=== RUN   TestAccComputeInstanceTemplate_IP
--- PASS: TestAccComputeInstanceTemplate_IP (50.13s)
=== RUN   TestAccComputeInstanceTemplate_networkIP
--- PASS: TestAccComputeInstanceTemplate_networkIP (24.77s)
=== RUN   TestAccComputeInstanceTemplate_disks
--- PASS: TestAccComputeInstanceTemplate_disks (25.09s)
=== RUN   TestAccComputeInstanceTemplate_subnet_auto
--- PASS: TestAccComputeInstanceTemplate_subnet_auto (107.73s)
=== RUN   TestAccComputeInstanceTemplate_subnet_custom
--- PASS: TestAccComputeInstanceTemplate_subnet_custom (89.12s)

[ghost]

I'm going to lock this issue because it has been closed for 30 days ⏳. This helps our maintainers find and focus on the active issues.

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