Clusters TaskManager Implementation

adds clusters taskmanager impl, with mongodb sharding as the first
implementation.

Co-Authored-By: amcrn <amcreynolds@ebaysf.com>
Co-Authored-By: rumale <rumale@ebaysf.com>

Partially implements: blueprint clustering

Change-Id: I39eeb7c58f454b26725d047107c52d716ff4df79
Merge "Clusters TaskManager Implementation"