Add customize diff for deprecated attribute on gc_policy

[ScottSuarez]

Adding customize diff when google_bigtable_gc_policy.max_age.days is equivalent to google_bigtable_gc_policy.max_age.duration.

resolves hashicorp/terraform-provider-google#8416

If this PR is for Terraform, I acknowledge that I have:

• Searched through the issue tracker for an open issue that this either resolves or contributes to, commented on it to claim it, and written "fixes {url}" or "part of {url}" in this PR description. If there were no relevant open issues, I opened one and commented that I would like to work on it (not necessary for very small changes).
• Generated Terraform, and ran make test and make lint to ensure it passes unit and linter tests.
• Ensured that all new fields I added that can be set by a user appear in at least one example (for generated resources) or third_party test (for handwritten resources or update tests).
• Ran relevant acceptance tests (If the acceptance tests do not yet pass or you are unable to run them, please let your reviewer know).
• Read the Release Notes Guide before writing my release note below.

Release Note Template for Downstream PRs (will be copied)

bigtable: fixed bug where gc_policy would attempt to recreate the resource when switching from deprecated attribute but maintaining the same value underlying value

[modular-magician]

Hi! I'm the modular magician. Your PR generated some diffs in downstreams - here they are.

Diff report:

Terraform GA: Diff ( 2 files changed, 101 insertions(+), 3 deletions(-))
Terraform Beta: Diff ( 2 files changed, 101 insertions(+), 3 deletions(-))

[modular-magician]

I have triggered VCR tests based on this PR's diffs. See the results here: "https://ci-oss.hashicorp.engineering/viewQueued.html?itemId=175325"

[melinath]

This LGTM. Just to make sure I'm understanding, it doesn't look like this tests whether there's a diff, just whether the change succeeds (but without the diff suppression it wouldn't succeed) - correct?

[melinath]

Looks like tests are failing:

Step #24 - "tpg-test": google/resource_bigtable_gc_policy.go:39:14: Error return value of `diff.Clear` is not checked (errcheck)
Step #24 - "tpg-test":      diff.Clear("max_age.0.days")
Step #24 - "tpg-test":                ^
Step #24 - "tpg-test": google/resource_bigtable_gc_policy.go:40:14: Error return value of `diff.Clear` is not checked (errcheck)
Step #24 - "tpg-test":      diff.Clear("max_age.0.duration")
Step #24 - "tpg-test":                ^
Step #23 - "tpgb-test": google-beta/resource_bigtable_gc_policy.go:39:14: Error return value of `diff.Clear` is not checked (errcheck)
Step #23 - "tpgb-test":       diff.Clear("max_age.0.days")
Step #23 - "tpgb-test":                 ^
Step #23 - "tpgb-test": google-beta/resource_bigtable_gc_policy.go:40:14: Error return value of `diff.Clear` is not checked (errcheck)
Step #23 - "tpgb-test":       diff.Clear("max_age.0.duration")
Step #23 - "tpgb-test":                 ^

[melinath]

I like the idea of unit tests for the diff suppress func, similar to TestDiskImageDiffSuppress - would you be open to adding some of those?

[modular-magician]

Hi! I'm the modular magician. Your PR generated some diffs in downstreams - here they are.

Diff report:

Terraform GA: Diff ( 2 files changed, 107 insertions(+), 3 deletions(-))
Terraform Beta: Diff ( 2 files changed, 107 insertions(+), 3 deletions(-))

[modular-magician]

I have triggered VCR tests based on this PR's diffs. See the results here: "https://ci-oss.hashicorp.engineering/viewQueued.html?itemId=175733"

[melinath]

auto-run failed. /gcbrun

[modular-magician]

Hi! I'm the modular magician. Your PR generated some diffs in downstreams - here they are.

Diff report:

Terraform GA: Diff ( 2 files changed, 107 insertions(+), 3 deletions(-))
Terraform Beta: Diff ( 3 files changed, 108 insertions(+), 4 deletions(-))

[modular-magician]

I have triggered VCR tests based on this PR's diffs. See the results here: "https://ci-oss.hashicorp.engineering/viewQueued.html?itemId=175737"

[modular-magician]

Hi! I'm the modular magician. Your PR generated some diffs in downstreams - here they are.

Diff report:

Terraform GA: Diff ( 3 files changed, 190 insertions(+), 6 deletions(-))
Terraform Beta: Diff ( 3 files changed, 190 insertions(+), 6 deletions(-))

[modular-magician]

I have triggered VCR tests based on this PR's diffs. See the results here: "https://ci-oss.hashicorp.engineering/viewQueued.html?itemId=175744"

[modular-magician]

Hi! I'm the modular magician. Your PR generated some diffs in downstreams - here they are.

Diff report:

Terraform GA: Diff ( 3 files changed, 190 insertions(+), 6 deletions(-))
Terraform Beta: Diff ( 4 files changed, 191 insertions(+), 7 deletions(-))

[modular-magician]

I have triggered VCR tests based on this PR's diffs. See the results here: "https://ci-oss.hashicorp.engineering/viewQueued.html?itemId=176357"

[modular-magician]

I have triggered VCR tests in RECORDING mode for the following tests that failed during VCR: TestAccApiGatewayGateway_apigatewayGatewayBasicExampleUpdated You can view the result here: "https://ci-oss.hashicorp.engineering/viewQueued.html?itemId=176363"

[modular-magician]

Tests failed during RECORDING mode: TestAccApiGatewayGateway_apigatewayGatewayBasicExampleUpdated Please fix these to complete your PR

[melinath]

LGTM - thanks for the tests!

[melinath]

I'm surprised this wasn't used anywhere... Could this be map[string]bool instead?