Shell helper `myPort()` assumes a single host:port from `getMongo().host`, however this may be a replicaset string under certain CI suites.   Split the string on commas first and use the host from the first member.

https://github.com/mongodb/mongo/blob/86e9d861dd056cdd71ff191ad032cc392bf9071a/src/mongo/shell/servers.js#L1435