Add a way to start an IT etcd server in go

Hello, 

I needed a way to make some integration tests with an etcd server. Instead of using an already running etcd server, I wanted to be able to start it in the test (via before and after test hooks). So, this is it

            s := NewItServer(4001)
            s.start()
            
            // Do your test with a go client (go-etcd for intstance)
            ....
            s.stop()

Hope this may help.