Add time based UUIDs

See #5941.


Using SecureRandom as a UUID generator is slow and doesn't allow us
to take adavantage of some lucene optimizations around ids with common
prefixes. This commit will allow us to use a
timestamp64bit-macAddr-counter UUID. Since the macAddr may be shared
among several nodes running on the same hardware we use an xor of the
macaddr with a SecureRandom number generated on startup.
That's a good question, honestly probably 2-3 bytes is fine we just need to test around expected levels of ntp timeslips at high indexing volumes. Since we don't inc the timestamp on slip, during a slip we may have a large number of events at the same timestamp. Perhaps we should just inc the timestamp on slip ?