ENG-4686 ability to choose different site agreement strategies
ENG-4686 clarifications, and improovements in site agreement
ENG-4686 added unit test for AgreementSeeker
ENG-4686 added more scenarios to TestMeshArbiter
ENG-4686 assertion fix in TestMeshArbiter
ENG-4686 tweaks in message handling and FailureSiteUpdateMessage matchers
ENG-4686 handle lone survivor case better