ENG-6735: @Promote kills the embedded AgentReceiver
Merge pull request #1607 from VoltDB/ENG-6735

ENG-6735: @Promote kills the embedded AgentReceiver
For ENG-6530, DR buffer should not have a tail, open transactions will be
moved to a new buffer.
For ENG-6530, refactor code to avoid redundancy. Discard empty buffers
after moving tail to new buffer. Modify testcase to adapt the new logic.
Disallow @UAC on replica unless running DR v2
Merge pull request #1627 from VoltDB/ENG-6530-new

Eng 6530 new
Merge dr-integration-prime into PersistentDrLog