[TACHYON-163]After 5 attempts we exit to avoid infinity retires

https://tachyon.atlassian.net/browse/TACHYON-163

Probably we should exit after attempts
If the connect method leads to infinity loop, user might think TahcyonWorker is fine with seeing the JVM process still existing.
But why exit?  There are two cases when register is called: on boot, master requests reregister.  If the worker is unable to connect to the master, this may be a temporary thing.  Killing the JVM in this case may be too much.  Tachyon worker shouldn't handle new requests, but killing itself doesn't seem like the right idea to me.