worker: Configurable timeout for RequestJob

This is backwards compatible, as long as the timeout is 0 (never
timeout), which is the default.

In case of the dbjobqueue the underlying timeout is due to
context.Canceled, context.DeadlineExceeded, or net.Error with Timeout()
true. For the fsjobqueue only the first two are considered.

internal/worker/client.go

@@ -5,6 +5,7 @@ import (
 	"context"
 	"crypto/tls"
 	"encoding/json"
+	"errors"
 	"fmt"
 	"io"
 	"net"
@@ -45,6 +46,8 @@ type Job interface {
 	UploadArtifact(name string, reader io.Reader) error
 }
 
+var ErrClientRequestJobTimeout = errors.New("Dequeue timed out, retry")
+
 type job struct {
 	client           *Client
 	id               uuid.UUID
@@ -185,6 +188,9 @@ func (c *Client) RequestJob(types []string, arch string) (Job, error) {
 	}
 	defer response.Body.Close()
 
+	if response.StatusCode == http.StatusNoContent {
+		return nil, ErrClientRequestJobTimeout
+	}
 	if response.StatusCode != http.StatusCreated {
 		return nil, errorFromResponse(response, "error requesting job")
 	}