ExportReviewNotes: Default to 2 threads

Not all systems have enough database connections in the connection
pool to support 2 threads per CPU. Exporting lots of changes doesn't
take that long, so 2 threads is acceptable.

Change-Id: I69bbade7f67023689ca54665833bc764d2d5503d
Signed-off-by: Shawn O. Pearce <sop@google.com>
2 files changed