Broker plugins (ACC) for performing resource brokering

Specialized brokers:

o Random

  The ExecutionTarget sorting is based on randomization, the PossibleTargets vector will be shuffled.

o FastestQueueBroker
  
  The sorting method is based on the shortest queue, where the number waiting jobs of is the lowest.

o Benchmark

  The sorting method is based on the fastest CPU, we use the CINT2000 (Integer Component of SPEC
  CPU2000) benchmark for this purpose , here are more information about this benchmark type:
  http://www.spec.org/cpu2000/CINT2000/

o Data

  The main idea was that the jobs should submit to that cluster where the data is. The sorting method is
  based on the A-REX file cache checking. There is a CacheCheck interface inside the A-REX which can be
  used to query whether files in question are present or not in the cache directory.

See src/hed/libs/compute/Submitter.cpp for implementation examples.
