Re-enable DNS service tests

[kobajagi]

Description

Upstream issues are solved now, this PR reverts #349

Checklist

(For exoscale contributors)

• Changelog updated (under Unreleased block)
• Acceptance tests OK
• For a new resource, datasource or new attributes: acceptance test added/updated

Testing

$ TF_ACC=1 go test ./... -run Domain
?       github.com/exoscale/terraform-provider-exoscale [no test files]
?       github.com/exoscale/terraform-provider-exoscale/pkg/config      [no test files]
?       github.com/exoscale/terraform-provider-exoscale/pkg/general     [no test files]
?       github.com/exoscale/terraform-provider-exoscale/pkg/provider    [no test files]
?       github.com/exoscale/terraform-provider-exoscale/pkg/provider/config     [no test files]
?       github.com/exoscale/terraform-provider-exoscale/pkg/resources/zones     [no test files]
?       github.com/exoscale/terraform-provider-exoscale/pkg/testutils   [no test files]
?       github.com/exoscale/terraform-provider-exoscale/pkg/utils       [no test files]
?       github.com/exoscale/terraform-provider-exoscale/pkg/validators  [no test files]
?       github.com/exoscale/terraform-provider-exoscale/pkg/version     [no test files]
?       github.com/exoscale/terraform-provider-exoscale/version [no test files]
ok      github.com/exoscale/terraform-provider-exoscale/exoscale        125.637s
ok      github.com/exoscale/terraform-provider-exoscale/pkg/filter      0.006s [no tests to run]
ok      github.com/exoscale/terraform-provider-exoscale/pkg/list        0.038s [no tests to run]
ok      github.com/exoscale/terraform-provider-exoscale/pkg/resources/anti_affinity_group       0.019s [no tests to run]
ok      github.com/exoscale/terraform-provider-exoscale/pkg/resources/block_storage     0.023s [no tests to run]
ok      github.com/exoscale/terraform-provider-exoscale/pkg/resources/database  0.020s [no tests to run]
ok      github.com/exoscale/terraform-provider-exoscale/pkg/resources/iam       0.020s [no tests to run]
ok      github.com/exoscale/terraform-provider-exoscale/pkg/resources/instance  0.018s [no tests to run]
ok      github.com/exoscale/terraform-provider-exoscale/pkg/resources/instance_pool     0.015s [no tests to run]
ok      github.com/exoscale/terraform-provider-exoscale/pkg/resources/nlb_service       0.015s [no tests to run]