The `read` implementation on my system doesn't know a `-n` parameter:
tools/usb-cdc-ecm/start_network.sh: 100: read: Illegal option -n
As the command is only used to block if no terminal is started, we can
as well remove them.
Optionally executes pyterm from CDC-ECM start_network.sh
The shell script exits and cleans up instantly unless there is a
blocking program running at the end. Users can supply a serial port to
display in pyterm, or alternatively just wait if it is a "headless"
deployment.