All: Prevent async tests from having multiple resume timeouts

[trentmwillis]

Addressing #984.

The root issue is that it was possible for a single async test to have multiple resumeProcessing timeouts. This parallel assert.async calls test is probably the easiest case to see why that would be a problem.

1. done1 would get called and queue up a resumeProcessing timeout.
2. done2 would get called and queue up another resumeProcessing timeout. test.semaphore is now at 0.
3. The first timeout executes and hits begin() to resume the test suite
4. The second timeout executes and hits begin() as well, which causes issues because we're already running

The reason this worked without passing in test before is that config.current would update between the time 3 and 4 happened above which would prevent begin() from getting called a second time.

My solution is to check to see if test is already waiting to resume when passed into resumeProcessing.

[gibson042]

👏

[trentmwillis]

@gibson042 updated.

[trentmwillis]

@gibson042 / @leobalter would appreciate a review so I can close this out.

[gibson042]

Sorry about dropping this. LGTM!

[leobalter]