Fix support for promise test less and anomaly less
grid.promise: do no write execution timestamp if running testless or anomalyless promise
grid.promise: send EmptyResult if promise is test less or anomaly less
There is now
EmptyResult object which is an empty promise result. This result is send if the promise test or anomaly was skiped (if disabled).
To prevent raise because
EmptyResult is unknonwn on old slapos-node with
slapos.core < 1.4.17 we will send an empty TestResult instead.