Fix bug: GPUs are not released in Reusable Training Service

[hzhua]

Because trial.environment is first released, it is always undefined.

nni/ts/nni_manager/training_service/reusable/trialDispatcher.ts

Lines 734 to 746 in 5eb43ea

	private releaseEnvironment(trial: TrialDetail): void {
	if (trial.environment !== undefined) {
	if (trial.environment.runningTrialCount <= 0) {
	throw new Error(`TrialDispatcher: environment ${trial.environment.id} has no counted running trial!`);
	}
	trial.environment.runningTrialCount--;
	trial.environment.latestTrialReleasedTime = Date.now();
	trial.environment = undefined;
	}
	if (true === this.enableGpuScheduler) {
	this.gpuScheduler.removeGpuReservation(trial);
	}
	}

The gpuScheduler will never release it because it requires trial.environment !== undefined

nni/ts/nni_manager/training_service/reusable/gpuScheduler.ts

Lines 99 to 104 in 5eb43ea

	public removeGpuReservation(trial: TrialDetail): void {
	if (trial.environment !== undefined &&
	trial.environment.defaultGpuSummary !== undefined &&
	trial.assignedGpus !== undefined &&
	trial.assignedGpus.length > 0) {

To fix this bug, this.gpuScheduler.removeGpuReservation(trial) should be executed at the beginning of releaseEnvironment