Avoid waitFor in scheduler termination code

why:
  Is reserved for main loop

nimbus/nimbus_desc.nim

@@ -64,7 +64,7 @@ proc stop*(nimbus: NimbusNode, conf: NimbusConf) {.async, gcsafe.} =
   if nimbus.peerManager.isNil.not:
     await nimbus.peerManager.stop()
   if nimbus.beaconSyncRef.isNil.not:
-    nimbus.beaconSyncRef.stop()
+    await nimbus.beaconSyncRef.stop()
   if nimbus.metricsServer.isNil.not:
     await nimbus.metricsServer.stop()
 

nimbus/sync/beacon.nim

@@ -68,8 +68,8 @@ proc init*(
 proc start*(desc: BeaconSyncRef): bool =
   desc.startSync()
 
-proc stop*(desc: BeaconSyncRef) =
-  desc.stopSync()
+proc stop*(desc: BeaconSyncRef) {.async.} =
+  await desc.stopSync()
 
 # ------------------------------------------------------------------------------
 # End

nimbus/sync/sync_sched.nim

@@ -160,7 +160,7 @@ proc key(peer: Peer): ENode =
 # Private functions
 # ------------------------------------------------------------------------------
 
-proc terminate[S,W](dsc: RunnerSyncRef[S,W]) =
+proc terminate[S,W](dsc: RunnerSyncRef[S,W]) {.async.} =
   ## Request termination and wait for sub-tasks to finish
   mixin runRelease
 
@@ -185,7 +185,7 @@ proc terminate[S,W](dsc: RunnerSyncRef[S,W]) =
     while dsc.daemonRunning:
       # Activate async job so it can finish
       try:
-        waitFor sleepAsync termWaitPollingTime
+        await sleepAsync termWaitPollingTime
       except CancelledError:
         trace "Shutdown: daemon timeout was cancelled", nWorkers=dsc.buddies.len
 
@@ -481,9 +481,9 @@ proc startSync*[S,W](dsc: RunnerSyncRef[S,W]): bool =
       return true
 
 
-proc stopSync*[S,W](dsc: RunnerSyncRef[S,W]) =
+proc stopSync*[S,W](dsc: RunnerSyncRef[S,W]) {.async.} =
   ## Stop syncing and free peer handlers .
-  dsc.terminate()
+  await dsc.terminate()
 
 
 proc isRunning*[S,W](dsc: RunnerSyncRef[S,W]): bool =