the nsupdate system test was intermittently failing due to the update
quota not being exceeded when it should have been. this is most likely
a timing issue: the client is sending updates too slowly, or the server
is processing them too quickly, for the quota to fill. this commit
attempts to make that the failure less likely by increasing the number
of update transactions from 10 to 20.
(cherry picked from commit 06b1faf068)
1d6721c5fa