Remove undesirable direct dependency on github.com/juju (istio#18427)

There remains some indirect dependencies on github.com/juju, those
will be addressed separately.

go.mod

@@ -94,7 +94,7 @@ require (
 	github.com/hashicorp/vault v0.10.0
 	github.com/howeyc/fsnotify v0.9.0
 	github.com/jefferai/jsonx v1.0.0 // indirect
-	github.com/juju/errors v0.0.0-20190207033735-e65537c515d7
+	github.com/juju/errors v0.0.0-20190207033735-e65537c515d7 // indirect
 	github.com/juju/loggo v0.0.0-20190212223446-d976af380377 // indirect
 	github.com/juju/testing v0.0.0-20190429233213-dfc56b8c09fc // indirect
 	github.com/keybase/go-crypto v0.0.0-20190416182011-b785b22cc757 // indirect

pkg/bootstrap/config.go

@@ -17,14 +17,14 @@ package bootstrap
 import (
 	"context"
 	"encoding/json"
+	"fmt"
 	"net"
 	"os"
 	"path"
 	"strings"
 	"time"
 
 	"github.com/gogo/protobuf/types"
-	"github.com/juju/errors"
 	"golang.org/x/oauth2/google"
 
 	meshAPI "istio.io/api/mesh/v1alpha1"
@@ -273,7 +273,7 @@ func getProxyConfigOptions(config *meshAPI.ProxyConfig, metadata *model.NodeMeta
 			// in-cluster credentials are fetched by using the GCE metadata server.
 			// You may also specify environment variable GOOGLE_APPLICATION_CREDENTIALS to point a GCP credentials file.
 			if cred, err = google.FindDefaultCredentials(context.Background()); err != nil {
-				return nil, errors.Errorf("Unable to process Stackdriver tracer: %v", err)
+				return nil, fmt.Errorf("unable to process Stackdriver tracer: %v", err)
 			}
 
 			opts = append(opts, option.StackDriverEnabled(true),