Bug 1373857

Description of problem:
When enable AutoUpdate and the new version is running, run "systemctl restart waagent", there's an error message "unexpectedly restarted" in the waagent.log

Version-Release number of selected component (if applicable):
WALinuxAgent-2.1.5

RHEL Version: RHEL-7.3-20160901.1
Python Version: 2.7.5

How reproducible:
100%

Steps to Reproduce:
1. Prepare a VM with WALA-2.1.5 installed.
2. Enable AutoUpdate inside the waagent.conf, and restart service, wait for AutoUpdate done:
# AutoUpdate.Enabled=y
# systemctl restart waagent
wait for several seconds. See this log inside the waagent.log:
INFO Event: name=WALinuxAgent, op=Enable, message=Agent WALinuxAgent-2.1.6 launched with command 'python -u bin/WALinuxAgent-2.1.6-py2.7.egg -run-exthandlers' is successfully running
3. Restart waagent manually
# systemctl restart waagent
4. Check waagent.log

Actual results:
There's error messages:

2016/09/07 17:10:26.272727 INFO WALinuxAgent-2.1.6 running as process 39426
2016/09/07 17:10:26.281475 INFO WALinuxAgent-2.1.6 unexpectedly restarted
2016/09/07 17:10:26.294560 ERROR Event: name=WALinuxAgent, op=Restart, message=WALinuxAgent-2.1.6 unexpectedly restarted

Expected results:
There's no error message.

Impact:
No function impact.

Additional info:
1. This issue is already fixed in the WALA-2.1.6 upstream release build. But we need to verify it in our official package.