Client: Search limit increased from 4 random DCs to 8 random DCs, plus nearest.
Server: Search factor increased from 3 to 5 times the bootstrap_expect.

This should allow for faster convergence in large environments (e.g.
sub-5min for 10K Consul DCs).

Per discussion, we want to be aggressive about fanning out vs possibly
fixating on only local DCs.  With RPC forwarding in place, a random walk
may be less optimal from a network latency perspective, but it is guaranteed
to eventually result in a converged state because all DCs are candidates
during the bootstrapping process.

…` tunable

…ack to Consul.

…cally.

It is perfectly viable for an admin to downsize a Nomad Server cluster
down to 1, 2, or `num % 2 == 0` (however ill-advised such activities
may be).  And instead of using `bootstrap_expect`, use a timeout-based
strategy.  If the `bootstrapFn` hasn't observed a leader in 15s it will
fall back to Consul and will poll every ~60s until it sees a leader.

Also don't attempt to join the Server with itself.