gofail: show error messages returned by gofail HTTP endpoints

Upon error, both PUT and DELETE will return an error message, which
would be nice for debugging if displayed.

Simplify `Enabled()` logic (linter suggestion)

Signed-off-by: Chun-Hung Tseng <henrybear327@gmail.com>

tests/framework/e2e/etcd_process.go

@@ -375,7 +375,11 @@ func (f *BinaryFailpoints) SetupHTTP(ctx context.Context, failpoint, payload str
 	}
 	defer resp.Body.Close()
 	if resp.StatusCode != http.StatusNoContent {
-		return fmt.Errorf("bad status code: %d", resp.StatusCode)
+		errMsg, err := io.ReadAll(resp.Body)
+		if err != nil {
+			return fmt.Errorf("bad status code: %d (%v)", resp.StatusCode, err)
+		}
+		return fmt.Errorf("bad status code: %d (%v)", resp.StatusCode, errMsg)
 	}
 	return nil
 }
@@ -404,17 +408,18 @@ func (f *BinaryFailpoints) DeactivateHTTP(ctx context.Context, failpoint string)
 	}
 	defer resp.Body.Close()
 	if resp.StatusCode != http.StatusNoContent {
-		return fmt.Errorf("bad status code: %d", resp.StatusCode)
+		errMsg, err := io.ReadAll(resp.Body)
+		if err != nil {
+			return fmt.Errorf("bad status code: %d (%v)", resp.StatusCode, err)
+		}
+		return fmt.Errorf("bad status code: %d (%v)", resp.StatusCode, errMsg)
 	}
 	return nil
 }
 
 func (f *BinaryFailpoints) Enabled() bool {
 	_, err := failpoints(f.member)
-	if err != nil {
-		return false
-	}
-	return true
+	return err == nil
 }
 
 func (f *BinaryFailpoints) Available(failpoint string) bool {