Reuse trace test servers when possible and fix flakiness of Trace_QPS .

[iantalarico]

• Reuses trace test servers when possible.
• Change the logic in Trace_QPS to be more robust.

These changes will reduce test run time and fix some test flakiness.

[evildour]

You may need to rebase master. AppVeyor has an error that the UploadObjectWithSessionUri snippet can't be found, which I just added in #890.

[evildour]

LGTM assuming the build issues are fixed. If you are already merged with the latest and there are still issues, ping me and I'll see if its something I caused.

[iantalarico]

@evildour I'm already merged with the latest bits, I'll take a closer look.

[iantalarico]

@evildour it looks like this failure started in #890. Although looking at the PR I'm not sure why. It looks correct.

[iantalarico]

@jskeet @evildour Getting off topic but I tried to build the docs locally but wasn't quite sure what to do. Do we have something to generate docfx.jsons?

[evildour]

I haven't tried building them locally, but I think I see what the problem is. About to submit a PR and will merge if it fixes the issue.

[jskeet]

Is there a risk of test interdependence by reusing the servers? I generally prefer the isolation given by each test having a separate srever - on the other hand, if it's causing issues either in terms of taking a long time or causing quota failures, I can see how this is desirable...

[iantalarico]

I don't think we will run into interdependence if we reuse the server as long as we clean the work space up. However, I also don't see a reason to reuse them if we don't have too.