Use log4j for elatic context related errors in EE.
Removed unused variables from ElasticContext.cpp.
Use log4j for errors in CopyOnWriteContext.cpp.
Merge pull request #920 from VoltDB/elastic-ee-log

Use log4j for elastic context related errors in EE.
Merge branch 'master' into ENG-5400

Conflicts:
	src/ee/storage/ElasticContext.cpp