A Tunnel Zone class

The tunnel zone class will be used by the agent to perform simulation. This
patch also includes tests to ensure that the conversion between the tunnel
zone proto and the Zoom object is done correctly.

Change-Id: I2939bf231ce80fb259211cc97d8d39bd13fef1e5
Signed-off-by: Nicolas Schiper <nicolas@midokura.com>
Merge "A Tunnel Zone class"