Fix asyncdispatch drain behavior (#14820) (#14838)

* Fix asyncdispatch drain behavior (#14820)

* Changed test to use asyncCheck instead of discard after code review (#14820)

* Added some debug statements to help understand what is happening in Azure.

* Removed debug statements and increased timeouts by 1 order of magnitude to account for slow Azure VMs

Co-authored-by: Ray Imber <ray@crankuptheamps.com>

tests/async/t14820.nim

@@ -0,0 +1,25 @@
+discard """
+output: '''
+iteration: 1
+iteration: 2
+iteration: 3
+iteration: 4
+async done
+iteration: 5
+'''
+"""
+
+import asyncdispatch, times
+
+var done = false
+proc somethingAsync() {.async.} =
+  yield sleepAsync 5000
+  echo "async done"
+  done = true
+  
+asyncCheck somethingAsync()
+var count = 0
+while not done:
+  count += 1
+  drain 1000
+  echo "iteration: ", count