redis commander: handle none redis_user

[YuryHrytsuk]

What do these changes do?

On some deployments we don't use REDIS_USER. This PR handles this case

FYI: @sanderegg

Related issue/s

• https://github.com/ITISFoundation/osparc-ops-environments/issues/241

Related PR/s

• https://github.com/ITISFoundation/osparc-ops-environments/pull/803

Checklist

• [X] I tested and it works