Raise an error when failing to retrieve RDS instance tags

[tomelliff]

Just logging the error means that if the user is unable to call the ListTagsForResource API endpoint then they will see a diff showing that they need to add the tags each time.
Instead it's better to actually error instead of hiding this from the user (unless they happen to check the logs).

Closes #345

See extended discussion in the original issue: hashicorp/terraform#9821

Fixes #345

Changes proposed in this pull request:

• Error instead of just logging when user is unable to call ListTagsForResource.

[bflad]

Looks great -- thanks @tomelliff! 🚀

21 tests passed (all tests)
=== RUN   TestAccAWSDBInstance_generatedName
--- PASS: TestAccAWSDBInstance_generatedName (281.67s)
=== RUN   TestAccAWSDBInstance_MinorVersion
--- PASS: TestAccAWSDBInstance_MinorVersion (392.89s)
=== RUN   TestAccAWSDBInstance_ec2Classic
--- PASS: TestAccAWSDBInstance_ec2Classic (432.98s)
=== RUN   TestAccAWSDBInstance_cloudwatchLogsExportConfiguration
--- PASS: TestAccAWSDBInstance_cloudwatchLogsExportConfiguration (447.04s)
=== RUN   TestAccAWSDBInstance_namePrefix
--- PASS: TestAccAWSDBInstance_namePrefix (453.29s)
=== RUN   TestAccAWSDBInstance_iamAuth
--- PASS: TestAccAWSDBInstance_iamAuth (453.52s)
=== RUN   TestAccAWSDBInstance_diffSuppressInitialState
--- PASS: TestAccAWSDBInstance_diffSuppressInitialState (453.65s)
=== RUN   TestAccAWSDBInstance_kmsKey
--- PASS: TestAccAWSDBInstance_kmsKey (472.94s)
=== RUN   TestAccAWSDBInstance_importBasic
--- PASS: TestAccAWSDBInstance_importBasic (483.75s)
=== RUN   TestAccAWSDBInstance_basic
--- PASS: TestAccAWSDBInstance_basic (544.30s)
=== RUN   TestAccAWSDBInstance_optionGroup
--- PASS: TestAccAWSDBInstance_optionGroup (544.95s)
=== RUN   TestAccAWSDBInstance_portUpdate
--- PASS: TestAccAWSDBInstance_portUpdate (548.42s)
=== RUN   TestAccAWSDBInstance_separate_iops_update
--- PASS: TestAccAWSDBInstance_separate_iops_update (589.74s)
=== RUN   TestAccAWSDBInstance_subnetGroup
--- PASS: TestAccAWSDBInstance_subnetGroup (594.72s)
=== RUN   TestAccAWSDBInstance_noSnapshot
--- PASS: TestAccAWSDBInstance_noSnapshot (634.19s)
=== RUN   TestAccAWSDBInstance_s3
--- PASS: TestAccAWSDBInstance_s3 (738.30s)
=== RUN   TestAccAWSDBInstance_enhancedMonitoring
--- PASS: TestAccAWSDBInstance_enhancedMonitoring (750.79s)
=== RUN   TestAccAWSDBInstance_cloudwatchLogsExportConfigurationUpdate
--- PASS: TestAccAWSDBInstance_cloudwatchLogsExportConfigurationUpdate (513.37s)
=== RUN   TestAccAWSDBInstance_snapshot
--- PASS: TestAccAWSDBInstance_snapshot (937.74s)
=== RUN   TestAccAWSDBInstance_replica
--- PASS: TestAccAWSDBInstance_replica (1384.06s)
=== RUN   TestAccAWSDBInstance_MSSQL_TZ
--- PASS: TestAccAWSDBInstance_MSSQL_TZ (1635.29s)

[bflad]

This has been released in version 1.25.0 of the AWS provider. Please see the Terraform documentation on provider versioning or reach out if you need any assistance upgrading.

[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.

If you feel this issue should be reopened, we encourage creating a new issue linking back to this one for added context. Thanks!