Reduce calls to Connect server

nuxeoctl should only update its cache on calls to high level APIs: mp-update, mp-add, mp-install...
Once the cache is updated, there should be no additional update during the processing, even if it takes more time than the cache expiration policy.

That would reduce the number of useless effective calls to the remote server.

When this is implemented, we must check the calls to the internal API from the Admin Center: an update is needed on listing display.