Installer should wait for network connectivity

[egeexyz]

If the installer runs before network connectivity is established, the pacstrap boostrap will fail with a misleading error about pacman mirrors.

The solution is simple: make the installer aware of network connectivity!

A simple MVP would be for the installer to check the outside world and exit gracefully if there's no connection.

A proper solution would be to check and sleep the install process for up to a minute until connectivity is established.