e2e: retry when a "transport is closing" error is hit

There have been occasional CI job failures due to "transport is closing"
errors. Adding this error to the isRetryableAPIError() function should
make sure to retry the request until the connection is restored.

Fixes: #2613
Signed-off-by: Niels de Vos <ndevos@redhat.com>

e2e/errors.go

@@ -41,6 +41,11 @@ func isRetryableAPIError(err error) bool {
 		return true
 	}
 
+	// "transport is closing" is an internal gRPC err, we can not use ErrConnClosing
+	if strings.Contains(err.Error(), "transport is closing") {
+		return true
+	}
+
 	return false
 }