[UI] Warning about self-signed certs is missing when node is joining the cluster

Seems like the "This cluster is using self-signed certificates. No peer verification between nodes will be done" warning is not shown anymore.
The warning should be shown on both addition scenarios: when addition is initiated by the cluster node, and when addition is initiated by the node to be added

UPDATE:
I noticed that on the-node-to-be-added the warning is actually shown sometimes, but incorrectly. Looks like that it currently looks at the presence of uploaded CA certificate, while it should look the node certificate instead. If the node certificate is 'generated', the warning should be shown. Presence of the uploaded CA cert alone is not enough to drop the warning.