Corrects some concurrency issues and exposes Master constructors for
tests to override
Quick and dirty pass at fault injection for enabling/disabling task
trackers
Restoring ModelClusterMap from master - Ben's compound status patch
references it so it's evidently still of some use.
Integrates Ben's patch for the compound status and propogating the details
of recommission/decommission failures up to the scale strategy for
handling.
Updates the corresponding model test to work with the specific semantics.
Restored call to enable before power on for consistency with current
master branch.
Expanded on the fault injection tests for node enable/disable.