ENG-5468: Use configured partition count to initialize the command log on join
node initialization.

The cartographer will only return partitions that are currently in the cluster,
which don't include the new partitions we are adding during joining node
initialization. Using the cartographer's partition count to initialize the
command log will have less partitions than expected.
Merge pull request #929 from VoltDB/ENG-5468

ENG-5468: Fix command log initialization on joining nodes