Add timeout for fetch file

    Currently, when fetch a file, the connection's connect timeout
    and read timeout is based on the default jvm setting, in this change, I change it to
    use spark.worker.timeout. This can be usefull, when the
    connection status between worker is not perfect. And prevent
    prematurely remove task set.

Author: Jiacheng Guo <guojc03@gmail.com>

Closes #98 from guojc/master and squashes the following commits:

abfe698 [Jiacheng Guo] add space according request
2a37c34 [Jiacheng Guo] Add timeout for fetch file     Currently, when fetch a file, the connection's connect timeout     and read timeout is based on the default jvm setting, in this change, I change it to     use spark.worker.timeout. This can be usefull, when the     connection status between worker is not perfect. And prevent     prematurely remove task set.