Consolidate code duplication and tests into a single lib package. Most of these functions were from various **/util.go functions that couldn't be imported due to cyclic imports. The consul/lib package is intended to be a terminal node in an import DAG and a place to stash various consul-only helper functions. Pulled in hashicorp/go-uuid instead of consolidating UUID access.
* A batch of updates is done all in a single transaction.
* We no longer need to get an update to kick things, there's a periodic flush.
* If incoming updates overwhelm the configured flush rate they will be dumped with an error.
