Try to use replSetGetConfig command before querying system collection and don't care about 'buildIndexes' property.

Changes:

- Don't wait for `buildIndexes` property in replica set configuration to match some hard-coded default.
- Try to use `replSetGetConfig` command first before querying local.system.replset for replica set configuration.

Mongo Orchestration was assuming that `buildIndexes` was always false. According to the [documentation](http://docs.mongodb.org/manual/reference/replica-configuration/#local.system.replset.members[n].buildIndexes), that may never have been true. Note that MO never actually configured replica sets with `buildIndexes: false`.
You can pass None as the second param for pop and not worry about the try block.