Moves the enforcement of delta as a magnitude in VMChoosers to the
methods where it's used. Made the checks uniform across implementations.
Corrected defect in DumbVMChooser.

Added a comment about uniqueness of queued events in VHM.
Adds additional logging, alters logging levels, extracts exception
messages, removes spurious stack traces.

IN-PROGRESS - task TA24337: Audit log statements: locations, levels and
data 
https://rally.eng.vmware.com/slm/detail/tk/7304800284