Shutdown stream snapshot data receiver thread when the snapshot it done.
ENG-3454: Fix NPE in @SystemInformation after rejoin.

For start actions that don't require catalog, @SystemInformation will throw NPE
afterwards when it tries to find the path to the catalog. Return null for the
path on the rejoined node.
Merge pull request #572 from VoltDB/fixes-for-elastic

Fix stream snapshot thread shutdown and @SystemInformation NPE