Initialize the scan total in nodediscover register

register_endpoint primes current but not total, so a first response
without a count field goes straight to

  UnboundLocalError: local variable 'total' referenced before assignment

on the elif.  Start at zero, which skips the progress line until the
server does report a count.

confluent_client/bin/nodediscover

@@ -53,6 +53,7 @@ columnmapping = {
 async def register_endpoint(options, session, addr):
     neednewline = False
     current = 0
+    total = 0
     async for rsp in session.update('/discovery/register', {'addresses': addr}):
         if 'count' in rsp:
             total = rsp['count']