Durable activity failures are not propagated to orchestrator in fan out/fan in pattern

At one point #572 was fixed with this pull request https://github.com/Azure/azure-functions-powershell-worker/pull/571.

If I do a single activity execution, the exception is propagated back up to the orchestrator. Good 👍

If I implement a fan out/fan in pattern like below, I don't get errors and only the activities that succeeded populate the `$tasks` variable.

``` Powershell
$ErrorActionPreference = "Stop"

$ParallelTasks = foreach ($file in $FailedFiles) {
# Create $FileDetails object
Invoke-DurableActivity -FunctionName "ProcessAuditFileActivity" -Input $FileDetails -NoWait
}

$tasks = Wait-DurableTask -Task $ParallelTasks

# 1 out of 2 tasks fails, $tasks only has one result and no errors from the failed activity, or exceptions thrown
```

Reproduce the fan-out/fan-in example using Invoke-DurableActivity with -NoWait and Wait-DurableTask, including one successful and one failing activity. Trace how the failed activity is represented when Wait-DurableTask returns, then verify that the durable failure reaches the orchestrator as an error while successful results remain available.

Written by the indexing model from the issue text.