[gbsyncd] exit with zero when platform has no gearbox (sonic-net#676)

Signed-off-by: Guohan Lu <lguohan@gmail.com>

syncd/scripts/gbsyncd_startup.py

@@ -19,6 +19,8 @@
 import os
 import sys
 import json
+import time
+import syslog
 import subprocess
 
 
@@ -39,7 +41,9 @@ def main():
  with open('/usr/share/sonic/hwsku/gearbox_config.json') as file_object:
  gearbox_config=json.load(file_object)
  except:
- sys.exit("No external PHY / gearbox supported on this platform, existing physycd application")
+ syslog.syslog(syslog.LOG_NOTICE, "No external PHY / gearbox supported on this platform, existing gbsyncd application")
+ time.sleep(2)
+ sys.exit(0)
 
  physyncd_enable(gearbox_config)