LSP mode does not auto-start hh_server

### HHVM Version

```
HipHop VM 4.0.4 (rel)
Compiler: 1565147373_N
Repo schema: fee5d293b5e21593fe0c45c410e57da563cdc8c4
```

(but I believe this repros on newer HHVM versions)

### Operating System and Version

Mac OS Mojave

### Standalone code, or other way to reproduce the problem

Open VSCode using the vscode-hack plugin in a workspace where hh_client/hh_server is not already running.

### Actual result

The LSP does not start hh_server. With tracing enabled, it logs this message:
```
Starting clientLsp at /private/tmp/hh_server/zSUserszSssandlerzSDocumentszSdevzSwebapp.client_lsp_log
For more detailed logs, try `tail -f $(hh_client --monitor-logname) $(hh_client --logname)`
Error: no hh_server running. Either start hh_server yourself or run hh_client without --autostart-server false
```

### Expected result

`--autostart-server` is the default for `hh_client`, and should likely be the default for `hh_client lsp` as well. This would automatically start the server, rather than requiring starting it manually on the CLI and reloading VSCode.