OpenTelemetry span status code does not map directly to google.rpc.Code

[aabmass]

Found a similar bug in JS and Python exporters (GoogleCloudPlatform/opentelemetry-operations-python#105)

Currently the code's int value is copied into the span pb if it's not Ok:

opentelemetry-operations-go/exporter/trace/trace_proto.go

Lines 117 to 119 in f9b9a4b

	if s.StatusCode != codes.Ok {
	sp.Status = &statuspb.Status{Code: int32(s.StatusCode), Message: s.StatusMessage}
	}

This is fine when it's Ok, but the actual error code mapping doesn't make sense:

• OTel Error Code = 1
• google.rpc.Code has CANCELLED = 1

[aabmass]

Actually on second look, this is not right for Ok either:

opentelemetry-operations-go/exporter/trace/trace_proto.go

Lines 120 to 122 in f9b9a4b

	if s.StatusCode == codes.Ok && s.StatusMessage != "" {
	sp.Status = &statuspb.Status{Code: int32(s.StatusCode), Message: s.StatusMessage}
	}

codes.Ok is 2 which is UNKNOWN = 2 error in the proto