ENG-4510: Construct rejoin task log after the directory is cleaned up.

The rejoin coordinator will clean up the directory, SPIs cannot construct rejoin
task logs before the directory is cleaned.
ENG-4510: Set rejoin type in RejoinProducer constructor so that it can correctly
construct task log later.
Merge pull request #433 from VoltDB/ENG-4510

ENG-4510: Fix live rejoin failures.

r=aweisberg