When the CI system supplies a .deps dir, use that as the lineups/packages resource source

Author: SteveSandersonMS

build/repo.props

@@ -7,4 +7,17 @@
   <PropertyGroup>
     <NuGetPublishFeed>https://dotnet.myget.org/f/aspnetcore-ci-dev</NuGetPublishFeed>
   </PropertyGroup>
+
+  <!--
+    If this build has a .deps dir supplied by the CI system, use that (and *only* that)
+    // to obtain the package lineup. This ensures we're building and testing against the
+    // specific Coherence build that this Templating repo build is chained to. 
+  -->
+  <PropertyGroup Condition="Exists('$(RepositoryRoot).deps\lineups')">
+    <PolicyRestoreSources>$(RepositoryRoot).deps\lineups</PolicyRestoreSources>
+  </PropertyGroup>
+  <ItemGroup Condition="Exists('$(RepositoryRoot).deps\build')">
+    <AdditionalRestoreSources Include="$(RepositoryRoot).deps\build" />
+  </ItemGroup>
+
 </Project>