Changes to loaded_upgrade test to improve reliability

* Wait for services after upgrading a node
* Remove hardcoded sleep call
* Reduce time between upgrades from 300 to 120 seconds
* Refactor worker functions to accept a report pid parameter instead
  of assuming a loaded_upgrade named process.
* Remove the mapreduce load. The results of the mapreduce queries
  during node shutdown are not predictable enough at this time to rely
  on for this test.
Merge pull request #505 from basho/refactor/loaded-upgrade-reliability

Changes to loaded_upgrade test to improve reliability