Mesos Fetcher file name output support (#6)

[ridv]

Description:

• Adding output filename to Mesos URI fetcher.

Testing Done:

• End to end tests.
• Integration tests.
• Submitted jobs with output filename included.
• Submitted jobs without output filename included.

[JustinVenus]

This looks good to me. It is simple and also a very useful feature I'd love to start using. Thanks for implementing this.