Prompt for a reboot if network configuration is changed.

With more care to unwind the current configuration this could be
removed.

Signed-off-by: David Scott <dave.scott@eu.citrix.com>
Limit the width of --yesno dialogs to 80 characters.

This should work better over serial consoles, which is
the common case.

Signed-off-by: David Scott <dave.scott@eu.citrix.com>