While I'm at it, add a DurationMinusBufferDomain() function to calculate the min/max for a given call to DurationMinusBuffer() in order to keep the implementation details self-contained.
used to schedule a TTL check. e.g.
d := lib.DurationMinusBuffer(60 * time.Duration, 10 * time.Second, 16)
will return a duration between 46.875s and 50s.
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.
