Add ReplicaSet tags for sharded environment
Test ReadPreference and ReadPreferenceTags over mongos
Add GLE with tags for RS and shards
Get rid of some code duplication and move the priority of the master

into make-servers rather then hardcoded in myconfig.js
Slight CS fixups after CR
Merged Pull Request #399

* pull-request/399:
  Slight CS fixups after CR
  Get rid of some code duplication and move the priority of the master
  Add GLE with tags for RS and shards
  Test ReadPreference and ReadPreferenceTags over mongos
  Add ReplicaSet tags for sharded environment