* A failure to allocate resources results in the embryonic dataset being
   destroyed. Previously, we would just leave it "unapproved". This means
   that, for a background lease creation, either the lease will eventually
   wind up in the "valid" state (success) or it will disappear (failure).

 * If creation fails early due to a policy violation, we exit with the
   value 2. Other early (non-background) exits will be 1 or -1 (255).
   This allows the a calling script to easily differentiate policy
   violations (for which the user might want to appeal via -U) from other
   more serious failures.