all: Tweak error creation (#6391)

- In the few places where we wrap errors, use the new Go 1.13 "%w"
  construction instead of %s or %v.

- Where we create errors with constant strings, consistently use
  errors.New and not fmt.Errorf.

- Remove capitalization from errors in the few places where we had that.

cmd/stcli/client.go

@@ -10,6 +10,7 @@ import (
 	"bytes"
 	"context"
 	"crypto/tls"
+	"errors"
 	"fmt"
 	"net"
 	"net/http"
@@ -80,16 +81,16 @@ func (c *APIClient) Post(url, body string) (*http.Response, error) {
 
 func checkResponse(response *http.Response) error {
 	if response.StatusCode == 404 {
-		return fmt.Errorf("Invalid endpoint or API call")
+		return errors.New("invalid endpoint or API call")
 	} else if response.StatusCode == 403 {
-		return fmt.Errorf("Invalid API key")
+		return errors.New("invalid API key")
 	} else if response.StatusCode != 200 {
 		data, err := responseToBArray(response)
 		if err != nil {
 			return err
 		}
 		body := strings.TrimSpace(string(data))
-		return fmt.Errorf("Unexpected HTTP status returned: %s\n%s", response.Status, body)
+		return fmt.Errorf("unexpected HTTP status returned: %s\n%s", response.Status, body)
 	}
 	return nil
 }

cmd/stcli/errors.go

@@ -7,6 +7,7 @@
 package main
 
 import (
+	"errors"
 	"fmt"
 	"strings"
 
@@ -54,7 +55,7 @@ func errorsPush(c *cli.Context) error {
 		if body != "" {
 			errStr += "\nBody: " + body
 		}
-		return fmt.Errorf(errStr)
+		return errors.New(errStr)
 	}
 	return nil
 }