fixed bug with nil result from uniq!

The providers lmhost and lmhostgroup, were taking advantage of the `uniq!` shortcut to get a unique array of items from an existing array. Unfortunately, `uniq!` returns `nil` when an array already consists of unique items. The `nil` response would then cause the `connections` array to remain unpopulated in `self.prefetch`. 
This change uses the standard `@array.uniq` method to pull the unique values from the array to build the `connections` array.