[keyserver] Do not verify identity logged for webapp and landing

Summary:
To avoid having to provide user credentials in remote terraform services for webapp and landing, we should only run identity login for non-landing and non-webapp nodes which is specified by running this on
only primary nodes (when unspecified, nodes are also primary) and secondary nodes.

Test Plan: terraform apply. On running landing and webapp nodes, I no longer receive errors about missing user credentials

Reviewers: varun, bartek, ashoat

Reviewed By: ashoat

Subscribers: tomek

Differential Revision: https://phab.comm.dev/D12927