Reduce the size of the UUID Lookup Length restriction from `8` to `2`.

I'm torn on this.  It's useful from a UX perspective for an operator to
be able to type in something that's short.  At the same time, by
enforcing an `8` character length, we reduced the probability of a user
depending on the behavior and having it suddenly stop working in the
future when a duplicate prefix is injected into the environment.

consul/state/catalog.go

@@ -13,7 +13,7 @@ const (
 	// minUUIDLookupLen is used as a minimum length of a node name required before
 	// we test to see if the name is actually a UUID and perform an ID-based node
 	// lookup.
-	minUUIDLookupLen = 8
+	minUUIDLookupLen = 2
 )
 
 // Nodes is used to pull the full list of nodes for use during snapshots.