Bug 1389218

This issue comes from github, which is reported by upstream wala users.

Description of problem: 
There are error logs if there's no new WALA package on Azure for AutoUpdate.

Version-Release number of selected component (if applicable): 
WALinuxAgent-2.2.0 

RHEL Version: RHEL-7.3 

How reproducible: 
100% 

Steps to Reproduce: 
1. Prepare a VM with WALA-2.2.0 installed and enable AutoUpdate feature
AutoUpdate.Enabled=y
AutoUpdate.GAFamily=Prod
# systemctl restart waagent
2. Wait for several seconds. Check waagent.log

Actual Result: 
There are error logs in waagent.log.

/var/log/waagent.log: 
2016/10/27 10:39:54.456491 WARNING Incarnation 1 failed to get Prod package list: (000008)Failed to fetch ExtensionManifest from all sources
2016/10/27 10:39:54.478181 ERROR Event: name=WALinuxAgent, op=Download, message=Incarnation 1 failed to get Prod package list: (000008)Failed to fetch ExtensionManifest from all sources

Expect Result: 
There's no error log.

Additional Info: 
The root cause is when there's no new WALA package on Azure "Prod" family, there's no URIs of "Prod" family in the ExtensionsConfig.xml file. If enable AutoUpdate feature, WALA will keep checking new wala versions(On restart and once per hour). It gets URI from ExtensionsConfig.n.xml file and then download the manifest.xml file, then get wala version list. If there's no URI of the configured family in the ExtensionsConfig.n.xml, WALA will log error message.

ExtensionsConfig.1.xml:
<?xml version="1.0" encoding="utf-8"?>^M
<Extensions version="1.0.0.0" goalStateIncarnation="1"><GuestAgentExtension xmlns:i="http://www.w3.org/2001/XMLSchema-instance">
  <GAFamilies>
    <GAFamily>
      <Name>Prod</Name>
      <Uris />
    </GAFamily>
    <GAFamily>
      <Name>Test</Name>
      <Uris>
        <Uri>https://rdfepirv2bl2prdstr01.blob.core.windows.net/7d89d439b79f4452950452399add2c90/Microsoft.OSTCLinuxAgent_Test_useast_manifest.xml</Uri>
        <Uri>https://rdfepirv2bl2prdstr02.blob.core.windows.net/7d89d439b79f4452950452399add2c90/Microsoft.OSTCLinuxAgent_Test_useast_manifest.xml</Uri>
        <Uri>https://rdfepirv2bl2prdstr03.blob.core.windows.net/7d89d439b79f4452950452399add2c90/Microsoft.OSTCLinuxAgent_Test_useast_manifest.xml</Uri>
        <Uri>https://rdfepirv2bl2prdstr04.blob.core.windows.net/7d89d439b79f4452950452399add2c90/Microsoft.OSTCLinuxAgent_Test_useast_manifest.xml</Uri>
        <Uri>https://rdfepirv2bl3prdstr01.blob.core.windows.net/7d89d439b79f4452950452399add2c90/Microsoft.OSTCLinuxAgent_Test_useast_manifest.xml</Uri>
        <Uri>https://rdfepirv2bl3prdstr02.blob.core.windows.net/7d89d439b79f4452950452399add2c90/Microsoft.OSTCLinuxAgent_Test_useast_manifest.xml</Uri>
        <Uri>https://rdfepirv2bl3prdstr03.blob.core.windows.net/7d89d439b79f4452950452399add2c90/Microsoft.OSTCLinuxAgent_Test_useast_manifest.xml</Uri>
        <Uri>https://zrdfepirv2bl4prdstr01.blob.core.windows.net/7d89d439b79f4452950452399add2c90/Microsoft.OSTCLinuxAgent_Test_useast_manifest.xml</Uri>
        <Uri>https://zrdfepirv2bl4prdstr03.blob.core.windows.net/7d89d439b79f4452950452399add2c90/Microsoft.OSTCLinuxAgent_Test_useast_manifest.xml</Uri>
        <Uri>https://zrdfepirv2bl5prdstr02.blob.core.windows.net/7d89d439b79f4452950452399add2c90/Microsoft.OSTCLinuxAgent_Test_useast_manifest.xml</Uri>
        <Uri>https://zrdfepirv2bl5prdstr04.blob.core.windows.net/7d89d439b79f4452950452399add2c90/Microsoft.OSTCLinuxAgent_Test_useast_manifest.xml</Uri>
        <Uri>https://zrdfepirv2bl5prdstr06.blob.core.windows.net/7d89d439b79f4452950452399add2c90/Microsoft.OSTCLinuxAgent_Test_useast_manifest.xml</Uri>
        <Uri>https://zrdfepirv2bl5prdstr09a.blob.core.windows.net/7d89d439b79f4452950452399add2c90/Microsoft.OSTCLinuxAgent_Test_useast_manifest.xml</Uri>
        <Uri>https://zrdfepirv2bl6prdstr02a.blob.core.windows.net/7d89d439b79f4452950452399add2c90/Microsoft.OSTCLinuxAgent_Test_useast_manifest.xml</Uri>
        <Uri>https://zrdfepirv2bl6prdstr05a.blob.core.windows.net/7d89d439b79f4452950452399add2c90/Microsoft.OSTCLinuxAgent_Test_useast_manifest.xml</Uri>
      </Uris>
    </GAFamily>
  </GAFamilies>
  <Location>eastus</Location>
</GuestAgentExtension>
<Plugins />
<StatusUploadBlob statusBlobType="BlockBlob">https://walaautoasmeastus.blob.core.windows.net/vhds/wala73depro.wala73depro.wala73depro.status?sr=b&amp;sp=rw&amp;se=9999-01-01&amp;sk=key1&amp;sv=2014-02-14&amp;sig=MBghJbzWAGux2LCcZv56wfUQY3c9mBhrohKX8tBGhC0%3D</StatusUploadBlob></Extensions>