SERVER-11239 Rename flag to allowDiskUse and include in error messages
SERVER-12284 Improve HostAndPort comparisons

* No longer copies strings to do the comparison
* Compares host strings once rather than twice in operator<
SERVER-12284 Rip ReplicaSetMonitor out of dbclient_rs files

This is pure code motion.
SERVER-12284 Rewrite ReplSetMonitor
SERVER-12284 Fix dbtests/replica_set_monitor_test.cpp for RSM rewrite
SERVER-12284 Simplify TagSet class

It is now little more than a well-typed BSONArray that has a more useful
default constructor.

Since the new RSM no longer uses the iterator portion of the API, it isn't
worth the cost of maintaining it. Additionally, TagSet being it's own iterator
was more than a little odd.
SERVER-12284 Make test wait for mongos to be aware of secondary.