Only log relevant storages in Praefect dial-nodes

Closes #2633 (closed)

This change introduces more targeted logging and diagnostics in the Praefect subcommand dial-nodes. Prior to this change, the tool would log all storages hosted by a Gitaly node. Now, it only checks the storages required to satisfy the virtual storage configuration. It also logs more accurately so that the user can identify which virtual storage pertains to a Gitaly storage.