cmd/registry/entity: Signer factory is not reused

[kostko]

The doInit (registry entity init subcommand) function creates two signer factory instances, where the first one is used to attempt to check if an entity already exists and the second one to actually generate an entity. In case a plugin signer is used, this results in two plugin processes to be spawned. If the plugin signer is hardware-backend, the first process may get exclusive access to the bus and operations on the second signer will all fail.