[VOL-1866] Changed module dependency to v12.0.0 of k8s client-go and v1.15.4 of k8s api/apimachinery in sync with other voltha components

Had to use pseudo-version corresponding to v12.0.0 of k8s client-go
because golang proxy is no longer serving the modules not complying
to Semantic Import Versioning rules including client-go v12.0.0.
Refer to https://github.com/kubernetes/client-go/issues/631 and
https://github.com/golang/go/issues/33558

Change-Id: I2e558bab7f0702f230761319eb5392a7d0532ea3
diff --git a/vendor/k8s.io/client-go/rest/request.go b/vendor/k8s.io/client-go/rest/request.go
index 64901fb..0570615 100644
--- a/vendor/k8s.io/client-go/rest/request.go
+++ b/vendor/k8s.io/client-go/rest/request.go
@@ -592,10 +592,15 @@
 		if result := r.transformResponse(resp, req); result.err != nil {
 			return nil, result.err
 		}
-		return nil, fmt.Errorf("for request '%+v', got status: %v", url, resp.StatusCode)
+		return nil, fmt.Errorf("for request %s, got status: %v", url, resp.StatusCode)
 	}
 	wrapperDecoder := wrapperDecoderFn(resp.Body)
-	return watch.NewStreamWatcher(restclientwatch.NewDecoder(wrapperDecoder, embeddedDecoder)), nil
+	return watch.NewStreamWatcher(
+		restclientwatch.NewDecoder(wrapperDecoder, embeddedDecoder),
+		// use 500 to indicate that the cause of the error is unknown - other error codes
+		// are more specific to HTTP interactions, and set a reason
+		errors.NewClientErrorReporter(http.StatusInternalServerError, r.verb, "ClientWatchDecoding"),
+	), nil
 }
 
 // updateURLMetrics is a convenience function for pushing metrics.
@@ -845,13 +850,13 @@
 			// 3. Apiserver closes connection.
 			// 4. client-go should catch this and return an error.
 			klog.V(2).Infof("Stream error %#v when reading response body, may be caused by closed connection.", err)
-			streamErr := fmt.Errorf("Stream error %#v when reading response body, may be caused by closed connection. Please retry.", err)
+			streamErr := fmt.Errorf("Stream error when reading response body, may be caused by closed connection. Please retry. Original error: %v", err)
 			return Result{
 				err: streamErr,
 			}
 		default:
-			klog.Errorf("Unexpected error when reading response body: %#v", err)
-			unexpectedErr := fmt.Errorf("Unexpected error %#v when reading response body. Please retry.", err)
+			klog.Errorf("Unexpected error when reading response body: %v", err)
+			unexpectedErr := fmt.Errorf("Unexpected error when reading response body. Please retry. Original error: %v", err)
 			return Result{
 				err: unexpectedErr,
 			}
@@ -1100,7 +1105,8 @@
 		return fmt.Errorf("serializer for %s doesn't exist", r.contentType)
 	}
 	if len(r.body) == 0 {
-		return fmt.Errorf("0-length response")
+		return fmt.Errorf("0-length response with status code: %d and content type: %s",
+			r.statusCode, r.contentType)
 	}
 
 	out, _, err := r.decoder.Decode(r.body, nil, obj)
@@ -1195,7 +1201,6 @@
 func ValidatePathSegmentName(name string, prefix bool) []string {
 	if prefix {
 		return IsValidPathSegmentPrefix(name)
-	} else {
-		return IsValidPathSegmentName(name)
 	}
+	return IsValidPathSegmentName(name)
 }