Update debian arm64 Helix queue image (#13009)

Update debian arm64 Helix queue image

docs/Helix.md

@@ -22,7 +22,7 @@ To run tests for the entire repo, run:
 .\eng\scripts\TestHelix.ps1
 ```
 
-This will restore, and then publish all of the test projects including some bootstrapping scripts that will install the correct dotnet runtime/sdk before running the test assemblies on the helix machine, and upload the job to helix, it won't wait for the jobs to complete, but you can go to https://mc.dot.net/#/user/$(your user name)/builds.
+This will restore, and then publish all of the test projects including some bootstrapping scripts that will install the correct dotnet runtime/sdk before running the test assemblies on the helix machine, and upload the job to helix.
 
 
 ## How do I look at the results of a helix run on Azure Pipelines?

eng/targets/Helix.Common.props

@@ -11,7 +11,7 @@
     <HelixAvailablePlatform Include="OSX" />
     <HelixAvailablePlatform Include="Linux" />
   </ItemGroup>
-    
+
     <!-- x64 queues -->
   <ItemGroup Condition="'$(IsWindowsOnlyTest)' != 'true' AND '$(TargetArchitecture)' == 'x64'">
     <HelixAvailableTargetQueue Include="Windows.10.Amd64.ClientRS4.VS2017.Open" Platform="Windows" />
@@ -27,11 +27,11 @@
     <HelixAvailableTargetQueue Include="Redhat.7.Amd64.Open" Platform="Linux" />
     <HelixAvailableTargetQueue Include="(Fedora.28.Amd64.Open)[email protected]/dotnet-buildtools/prereqs:fedora-28-helix-09ca40b-20190508143249" Platform="Linux" />
   </ItemGroup>
-    
+
   <ItemGroup Condition="'$(IsWindowsOnlyTest)' != 'true' AND '$(TargetArchitecture)' == 'arm64'">
     <!-- arm64 queues -->
-    <HelixAvailableTargetQueue Include="(Debian.9.Arm64.Open)[email protected]/dotnet-buildtools/prereqs:debian-9-helix-arm64v8-0a0ebdd-20190312215438" Platform="Linux" />
-    
+    <HelixAvailableTargetQueue Include="(Debian.9.Arm64.Open)[email protected]/dotnet-buildtools/prereqs:debian-9-helix-arm64v8-a12566d-20190807161036" Platform="Linux" />
+
     <!-- Need to resolve permission issues on this docker queue
     <HelixAvailableTargetQueue Include="(Alpine.38.Arm64)[email protected]/dotnet-buildtools/prereqs:alpine-3.8-helix-arm64v8-46e69dd-20190327215724" Platform="Linux" />
     <HelixAvailableTargetQueue Include="(Ubuntu-1804.Arm64.Open)[email protected]/dotnet-buildtools/prereqs:ubuntu-18.04-helix-arm64v8-6f28fa9-20190606004102" Platform="Linux" />