Don't request MongoDB recordStats

Disables the recordStats output which was introduced in MongoDB 2.4 and
causes a read lock, which can slow down agent execution and have an
effect on the mongod server itself.

http://docs.mongodb.org/manual/reference/command/serverStatus/#server-st
atus-recordstats

Requested in https://serverdensity.zendesk.com/agent/#/tickets/857