Confirmation of registration in free_mon_rs_resend.js may race with registration

The primary's webserver is instructed to return a re-registration request on the third metrics upload. When this happens, it persists a document to disk which describes free monitoring being in the pending state, which gets replicated to the secondary. While the secondary has this document, it will display the "pending" state in serverStatus. The test has a race, where it will wait for one registration on the primary and secondary, then check serverStatus. It is possible for the primary to make three metrics uploads, and get the re-registration request before the serverStatus is validated.