Fix nodediscover clear

Nested async iteration of multiple confluent calls fail, break
it into two distinct queries.

confluent_client/bin/nodediscover

@@ -270,7 +270,8 @@ async def list_discovery(options, session):
             print(row)
 
 async def clear_discovery(options, session):
-    async for mac in list_matching_macs(options, session):
+    allmacs = [x async for x in list_matching_macs(options, session)]
+    for mac in allmacs:
         async for res in session.delete('/discovery/by-mac/{0}'.format(mac)):
             if 'deleted' in res:
                 print('Cleared info for {0}'.format(res['deleted']))

confluent_server/confluent/discovery/core.py

@@ -1615,9 +1615,7 @@ async def rescan():
     if scanner:
         return
     else:
-        print("begin")
         scanner = util.spawn(blocking_scan())
-        print("bg")
     await remotescan()
 
 async def remotescan():