This changes the behaviour of `aws_api_gateway_integration` to set the
`passthrough_behaviour` to be computed as this was breaking the import
test
```
% make testacc TEST=./builtin/providers/aws TESTARGS='-run=TestAccAWSAPIGatewayApiKey_importBasic'
==> Checking that code complies with gofmt requirements...
go generate $(go list ./... | grep -v /terraform/vendor/)
TF_ACC=1 go test ./builtin/providers/aws -v
-run=TestAccAWSAPIGatewayApiKey_importBasic -timeout 120m
=== RUN TestAccAWSAPIGatewayApiKey_importBasic
--- PASS: TestAccAWSAPIGatewayApiKey_importBasic (50.19s)
PASS
ok github.com/hashicorp/terraform/builtin/providers/aws 50.210s
```
```
% make testacc TEST=./builtin/providers/aws TESTARGS='-run=TestAccAWSAPIGatewayIntegration_'
==> Checking that code complies with gofmt requirements...
go generate $(go list ./... | grep -v /terraform/vendor/)
TF_ACC=1 go test ./builtin/providers/aws -v
-run=TestAccAWSAPIGatewayIntegration_ -timeout 120m
=== RUN TestAccAWSAPIGatewayIntegration_basic
--- PASS: TestAccAWSAPIGatewayIntegration_basic (67.43s)
PASS
ok github.com/hashicorp/terraform/builtin/providers/aws 67.449s
```
Change the `RetryFunc` from a plain `error` return type to a
specialized `RetryError` which must decide whether it is
retryable or not.
Add `RetryableError` / `NonRetryableError` factory functions that
callers are meant to use to build up these errors.
This makes it eminently clear whether or not a given error is
retryable from inside the client code.
Goal here is to _not_ change any behavior, simply reflect the
existing behavior with the new, clearer, API.