Disable keep alive checks in long polling transport

#3259
This PersistentConnection being used is called EchoConnection. The PersistentConnection has nothing to do specifically with encoding JSON.

I think it might have made sense to name the endpoint "autoencodedjson" when it was only used for "transport auto JSON encodes messages correctly when sending" test. But since then it has been used by the "ConnectionFunctionsCorrectlyAfterCallingStartMutlipleTimes" functional test, and now I am using it in my "Polls exceeding the ConnectionTimeout will trigger a reconnect" test.

I think it could be a little confusing to name a path after just one of three tests that happen to use it, so I renamed it.