MEDIUM: tools: use the hashed random pair for UUID generation

MEDIUM: tools: use the hashed random pair for UUID generation

The UUID generation used to emit the internal PRNG state, which allows
to predict previous and next ones, or disclose the internal PRNG state.
While not critical, it may eventually become an issue.

This patch uses the new ha_random64_pair_hashed() function that returns
a pair of u64 that are hashed from the internal PRNG state. It's almost
twice as fast on 20 threads (14.1M UUID/s vs 7.8M/s).