Improve tot request code

Handling some cases where `err` asignment would not have happened
correctly and the error would have been dropped, as well as using an
exponential backoff and reducing the total number of retries done.

Signed-off-by: Steve Kuznetsov <skuznets@redhat.com>

prow/pjutil/jobspec.go

@@ -23,6 +23,7 @@ import (
 	"io/ioutil"
 	"net/http"
 	"os"
+	"path"
 	"strconv"
 	"time"
 
@@ -63,10 +64,12 @@ func NewJobSpec(spec kube.ProwJobSpec, buildId, prowJobId string) JobSpec {
 // to vend build identifier for the job
 func GetBuildID(name, totURL string) (string, error) {
 	var err error
-	url := totURL + "/vend/" + name
-	for retries := 0; retries < 60; retries++ {
+	url := path.Join(totURL, "vend", name)
+	sleep := 100 * time.Millisecond
+	for retries := 0; retries < 10; retries++ {
 		if retries > 0 {
-			time.Sleep(2 * time.Second)
+			time.Sleep(sleep)
+			sleep = sleep * 2
 		}
 		var resp *http.Response
 		resp, err = http.Get(url)
@@ -75,9 +78,12 @@ func GetBuildID(name, totURL string) (string, error) {
 		}
 		defer resp.Body.Close()
 		if resp.StatusCode != 200 {
+			err = fmt.Errorf("got unexpected response from tot: %v", resp.Status)
 			continue
 		}
-		if buf, err := ioutil.ReadAll(resp.Body); err == nil {
+		var buf []byte
+		buf, err = ioutil.ReadAll(resp.Body)
+		if err == nil {
 			return string(buf), nil
 		}
 		return "", err