Merge #472

472: feat(http): Distinct app and internal error codes in the handleError function r=48d90782 a=48d90782

This PR introduces distinct error codes for the app and internal RR errors.
Errors: 
```go
roadrunner.ErrNoAssociatedPool
roadrunner.ErrAllocateWorker
roadrunner.ErrWorkerNotReady
roadrunner.ErrEmptyPayload
roadrunner.ErrPoolStopped
roadrunner.ErrWorkerAllocateTimeout
roadrunner.ErrAllWorkersAreDead
```
now associated with the internal error codes. All other errors are application errors.
Some types of errors are impossible to distinguish in the RR1, for example `json.Unmarshall` internal error or similar.
The `.rr.yaml` now contain two more options for the errors.
```yaml
http:
    internalErrorCode: 502,
    appErrorCode: 502
```
Default behavior unchanged (500 error code as before), but now might be overridden.
closes #471 

Co-authored-by: Valery Piashchynski <[email protected]>

1 files changed, 2 insertions, 1 deletions

diff --git a/server_test.go b/server_test.go
index 9ab480b1..a8d52856 100644
--- a/server_test.go
+++ b/server_test.go
@@ -1,11 +1,12 @@
 package roadrunner
 
 import (
-	"github.com/stretchr/testify/assert"
 	"os/exec"
 	"runtime"
 	"testing"
 	"time"
+
+	"github.com/stretchr/testify/assert"
 )
 
 func TestServer_PipesEcho(t *testing.T) {