Improvements to MongoDB replica sets

* Replica set class is Iterable<MongoDBServer>
* Replica set entity sets state to on fire if first server up fails to
  initiate the set
* Logging in MongoClientSupport improved when command result was not ok.
Switch Iterable<MongoDBServer> for getReplicas() method
Merge pull request #1097 from sjcorbett/mongodb-tweaks

Small improvements to MongoDB replica sets
collect more sensors for mongo, and add a ResilientMongoApp; also let the default isRunning check fail more quickly (so failures are picked up sooner, as isRunning is done on restart, and clouds which black-hole ssh will cause the max timeout to occur, time num ssh retries (4) ); and also misc tidies to other items (mainly deprecation)
apply code review from #1118
Merge pull request #1118 from ahgittin/mongo

collect more sensors for mongo, and add a ResilientMongoApp
Merge branch 'master' into feature/yaml