fix(retrofit): use SpinnakerServerException.getHttpMethod() instead of reflection in SpinnakerServerExceptionHandler

[alice485]

BaseRetrofitExceptionHandler's retry behavior uses a method called findHttpMethodAnnotation to retrieve an exception's HTTP method. For retrofit2 exceptions, this method no longer works due to things being annotated differently in retrofit2. However, Spinnaker*Exceptions can use getHttpMethod() to retrieve this value, so this PR updates the exception handler to default to using the getter and only use findHttpMethodAnnotation if the getter returns null.

[dbyron-sf]

I'm seeing a number of failures with only the commit that adds the tests, but not the code changes. Ideally there wouldn't be any failures, and the code change commit would adjust the tests so the behavior change is clear. I realize this is a lot to ask. I am quite curious what we're actually fixing in this PR though.

[alice485]

I'm seeing a number of failures with only the commit that adds the tests, but not the code changes. Ideally there wouldn't be any failures, and the code change commit would adjust the tests so the behavior change is clear. I realize this is a lot to ask. I am quite curious what we're actually fixing in this PR though.

Basically, the point of this PR was to avoid using reflection unless the exception was created from a RetrofitError, since otherwise we can simply use SpinnakerServerException.getHttpMethod().

During that process, I found that the exception handler's shouldRetry method always returns false (except in the case of a 503 response) for retrofit2 exceptions since it won't be able to find the http method annotation in the stack trace. I mentioned why this is the case here.

So adding retrofit2 exceptions to the parameters being passed into the tests would necessarily make them fail, which is why I originally added both the test exceptions and the code changes in the same commit.

[dbyron-sf]

It would be nice to see the behavior changes in detail, but I'll get over it. Would you mind changing the PR title / commit message to be fix instead of refactor though, and say that what we're fixing is retry behavior for retrofit2?