cve-update-nvd2-native: retry all errors and sleep between retries

cve-update-nvd2-native: retry all errors and sleep between retries

Last couple days it is not possible to update NVD DB as servers
are returning lot of errors.
Mostly "HTTP Error 503: Service Unavailable" is observed but
sporadially also some others.

Retrying helps in most cases, so extend retries to all errors.

Additionally add sleep which is recommended by NVD between requests.
These retries are already implemented between successful requests,
but giving servers time between failed ones is important, too.

Signed-off-by: Peter Marko <peter.marko@siemens.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>