hostgw: Check existence of and compare routes before attempting to add/update them
hostgw: Check existence of and compare routes before attempting to add/update them

Closes a bug where hostgw.network.rl (route list) would be out of
sync with the host system in case of startup with existing routes.

Gives hostgw the ability to update existing routes that does not
match configuration.

Improves usability by avoiding to log non-errors to the user.

coreos/flannel,adiclepcea/flannel,coreos/flannel,adiclepcea/flannel,adiclepcea/flannel,coreos/flannel