VPNLog: Add timestamps to emailed logs

This helps to show which events occurred in close proximity to the
failure (versus events that happened 20 minutes earlier).

Signed-off-by: Kevin Cernekee <cernekee@gmail.com>
KeepAlive: First attempt at DNS based probes

Wake up to generate traffic every few minutes to keep the connection
from timing out.

Signed-off-by: Kevin Cernekee <cernekee@gmail.com>