public PrepareResult deployResult() {
        if (activationFailure != null) throw activationFailure;
        return prepareResult;
    }
Allows a partial deployment success, where the application is prepared, but not activated.
This currently only allows the parent-host-not-ready and application-lock cases, as other transient errors are
thrown too early (LB during prepare, cert during validation), but could be expanded to allow
reuse of a prepared session in the future. In that case, users of this result (handler and its client)
must also be updated.

@author jonmv
configserver/src/main/java/com/yahoo/vespa/config/server/http/v2/PrepareAndActivateResult.java