dotnet-trace CLI output doesn't update under low frequency events

[sywhang]

If you turn on dotnet-trace with a provider that's not verbose, it doesn't update the CLI window because the Task that prints to the console is stuck on the Read() call.

To repro this, try turning off SampleProfiler and just Microsoft-Windows-DotNETRuntime provider with a keyword that's not very frequent - for example, on an app that doesn't allocate anything and turn on just the GC keyword.

[noahfalk]

This a minor UI issue, lowering priority