SHDP-440 Fix anomalies in DefaultAllocateCountTracker

- Fix some wrong type of tracking for mix of racks and hosts.
- Also adresses SHDP-441.
- NOTE: we don't actually get trouble with these bugs, afaik,
  because internally we use different DefaultAllocateCountTrackers
  for mixed hosts and racks due to fact that with yarn those
  cannot be mixed on an allocation request level. Anyway, it's good
  to fix these small problems.