Consistent behaviour w.r.t. the `server_managed` flag

[thobson88]

When the NavigatorArgs.server_managed is false, all server operations should be skipped and this should be reflected in the log messages.

Currently this isn't the case. There are some cases where:

• the server is started unnecessarily,
• the pause to await server shut down happens unnecessarily
• log messages are determined by the --parallel flag.