unnecessary hftp token fetch and renewal thread

Instantiation of the hftp filesystem is causing a token to be implicitly created and added to a custom token renewal thread. With the new token renewal feature in the JT, this causes the mapreduce obtainTokensForNamenodes to fetch two tokens (an implicit and uncancelled token, and an explicit token) and leave a spurious renewal thread running. This thread should not be running in the JT.

After speaking with Owen, the quick solution is to lazy fetch the token, and to lazy start the renewer thread.