Mark --assets_path as deprecated.
Mark --assets_path as deprecated.

Summary: Fixes the missing documentation part of https://github.com/mesosphere/marathon/issues/3706#issuecomment-255448662

Test Plan: read

Reviewers: unterstein, jeschkies

Reviewed By: jeschkies

Subscribers: marathon-team

Differential Revision: https://phabricator.mesosphere.com/D169

Caerostris/marathon,meln1k/marathon,meln1k/marathon,janisz/marathon,Caerostris/marathon,natemurthy/marathon,natemurthy/marathon,guenter/marathon,mesosphere/marathon,mesosphere/marathon,meln1k/marathon,guenter/marathon,gsantovena/marathon,gsantovena/marathon,natemurthy/marathon,Caerostris/marathon,mesosphere/marathon,Caerostris/marathon,guenter/marathon,guenter/marathon,janisz/marathon,janisz/marathon,gsantovena/marathon,mesosphere/marathon,gsantovena/marathon,guenter/marathon,gsantovena/marathon,meln1k/marathon,janisz/marathon,janisz/marathon,mesosphere/marathon,Caerostris/marathon,meln1k/marathon