I'm not sure that there's a way to log out (someone correct me if there is), but you can go under Settings > Google > select your email under Accounts, then click the three dots on the upper right an choose Remove Account. This should detach your account from the device.
Alternatively if you use the 2-step verification through Google you can create a password specifically for the N7 then revoke that password when you want to disconnect the N7 from your account. That's probably the better option since you can 'log out' even if you don't have the device in hand.