Implement proposal 221: Stop sending CREATE_FAST

This makes FastFirstHopPK an AUTOBOOL; makes the default "auto"; and
makes the behavior of "auto" be "look at the consensus."
circuit_build_failed: distinguish "first hop chan failed", "CREATE failed"

Roger spotted this on tor-dev in his comments on proposal 221.

(Actually, detect DESTROY vs everything else, since arma likes
network timeout indicating failure but not overload indicating failure.)