UI doesn't start if network manager not found

[benfrancis]

STR:

• Install krellian-kiosk snap on Ubuntu Core without network-manager snap installed
• Start krellian-kiosk snap

Expected:

• UI starts even though network management functions not available

Actual:

• UI gets stuck on a white screen

[benfrancis]

Note: Can catch uncaught exceptions in Electron/Node.js to prevent the gtkDialog from showing, but it doesn't prevent the process from exiting.

process.on("uncaughtException", (error) => {
   console.error(error);
});

[benfrancis]

Might be useful https://git.launchpad.net/~snappy-hwe-team/snappy-hwe-snaps/+git/wifi-connect/tree/netman/dbus.go#n741