Update version to be derived from timestamps.
Update version to be derived from timestamps.

Summary:
Change deb version to be derived from timestamp of latest commit instead of commit number.
Also show commit SHA for easy debugging.

Test Plan: Created new deb

Reviewers: kylec, jhance

Reviewed By: jhance

Differential Revision: https://tails.corp.dropbox.com/D128570

dropbox/changes-mesos-framework,dropbox/changes-mesos-framework