fixes #8261 - use Default Organization for certificate org

Hmm, well...the capsule installer presents the org option like this:

    --org  Org attribute for managed certificates (default: "SomeOrg")

A capsule will be a content host, and a content host can only belong to one org, so why not relate the two org items?  

Basically, my argument is: why would I expect to get a subscription-manager command to copy and paste that says `Default Organization` if I run 'capsule-certs-generate --org="Stephens_Widgets"'?