SERVER-15424 Age out old connections used by replication for communicating with other members.

By capping the lifetime of connections used for heartbeats at 30 seconds, we
ensure that DNS and firewall changes that only affect new connections eventually
impact nodes' belief about the reachability of other nodes in the replica set.
SERVER-16457 Temporarily assume verify returning EBUSY means everything is fine
Merge remote-tracking branch 'upstream/master'