Introduced Master <-> Slave reconciliation.

Review: https://reviews.apache.org/r/26206
Split out partition and reconciliation tests from FaultTolerace tests.

Review: https://reviews.apache.org/r/26207
Added a test for the Master <-> Slave reconciliation race.

Review: https://reviews.apache.org/r/26208
Disallowed duplicate module names.

Module manager should return error on encountering a duplicate module
name (i.e. if a module with the same name has already been loaded).

Review: https://reviews.apache.org/r/26513