Refactoring of logging
* removed apache-commons logging (was only wrapping other implementation)
* all logging in RadarGun should go through org.radargun.logging.Log
* support for log4j (default) and log4j2 (when compiling with -Dlog4j2)
* added per node rolling appender and default configuration for log4j2
* jboss-logging is excluded from Infinispan dependencies, version 3.1.4.GA explicitely provided (prior versions don't support log4j2)
Fix: pooled keys array should not be allocated for poolKeys = false
Topology events:
* fixed checking history for topology events
* formatted dates in topology events
Background stressors tests:
* waiting until all operations are checked (and resuming afterwards)
* stressors may ignore that checkers on dead nodes have not checked everything
  (this is important for elasticity tests where we may end up with single node)