Pass artifact-search-path to changes-client in default/Mesos
Pass artifact-search-path to changes-client in default/Mesos

Summary:
- Without this the search path is just always "/home/ubuntu", so setting
  a project path that's not a relative directory won't collect any artifacts.

Test Plan: None

Reviewers: kylec

Reviewed By: kylec

Subscribers: changesbot

Differential Revision: https://tails.corp.dropbox.com/D158768

dropbox/changes,dropbox/changes,dropbox/changes,dropbox/changes