CouchDB bulk updates should allow a configurable max batch size.
Http requests with an excessive size could cause failures.

Max batch size should be configurable in core.yaml along with other
CouchDB config settings.

Change-Id: Ifa6222dae8d2ca6a3d7dca44642091ecc4c4ab81
Signed-off-by: Chris Elder <chris.elder@us.ibm.com>