Allow logging to a file via a cli flag

[SEJeff]

Placeholder for this issue in chaos. From an ops standpoint, this is something that I see as lacking a bit on marathon. It would be really nice if there was a way to have it log to a file for those running it standalone and not inside a docker container.

[meichstedt]

Note: This issue has been migrated to https://jira.mesosphere.com/browse/MARATHON-2136. For more information see https://groups.google.com/forum/#!topic/marathon-framework/khtvf-ifnp8.