Expose trove conductor manager class as conf property

The current implementation of trove conductor hard-codes the conductor
manager class name in the cmd entry point thus not allowing it to be set
by consumers. This change exposes that classname on the conductor conf
so that consumers could plug-in their own manager class. Additionally
unit tests are provided to ensure a user defined and conductor manager
can be used in addition to the default trove conductor manager.

Change-Id: I6bf88dd9cf119f0eb6a197f4bda48c309511297e
Implements: blueprint pluggable-conductor-manager
Merge "Expose trove conductor manager class as conf property"