MB-12948 completely idle goxdcr (no replications) on completely idle single-node cluster burns 100% of cpu

Change-Id: I79ed09e945834193e6dc1696074d987279916861
Reviewed-on: http://review.couchbase.org/44413
Reviewed-by: Yu Sui <ysui68@gmail.com>
Tested-by: Xiaomei Zhang <xiaomeizhangatwork@gmail.com>