test(server_test.go) Fix a deadlock.
We stop all the servers before finishing the MultiNode test. The mock transporter directly calls to the function of the target server. If the target is stopped, the transporter will just hang there waiting for a reply. So the sender server will also hang for a reply. We add a timeout for the reply to solve this problem.
Merge pull request #148 from xiangli-cmu/fix_test

test(server_test.go) Fix a deadlock.