Fix Issue #40

Will now check if either the private or the public ip is already in the
the list of squid nodes. If so, the load value will be updated and time
since last heartbeat will be reset to 0.
Fix Issue #39

Shoal-agent will now log at info level on start and exit (running as a
service or normally) and will log at debug level every time it sends a
message to the shoal-server.