Update dependencies from https://github.com/dotnet/arcade build 20191211.6 (#5871)

- Microsoft.DotNet.Arcade.Sdk - 5.0.0-beta.19611.6

eng/common/tools.ps1

@@ -98,7 +98,7 @@ function Exec-Process([string]$command, [string]$commandArgs) {
   }
 }
 
-function InitializeDotNetCli([bool]$install) {
+function InitializeDotNetCli([bool]$install, [bool]$createSdkLocationFile) {
   if (Test-Path variable:global:_DotNetInstallDir) {
     return $global:_DotNetInstallDir
   }
@@ -146,6 +146,22 @@ function InitializeDotNetCli([bool]$install) {
     }
 
     $env:DOTNET_INSTALL_DIR = $dotnetRoot
+
+    if ($createSdkLocationFile) {
+      # Create a temporary file under the toolset dir and rename it to sdk.txt to avoid races.
+      do { 
+        $sdkCacheFileTemp = Join-Path $ToolsetDir $([System.IO.Path]::GetRandomFileName())
+      } 
+      until (!(Test-Path $sdkCacheFileTemp))
+      Set-Content -Path $sdkCacheFileTemp -Value $dotnetRoot
+
+      try {
+        Rename-Item -Force -Path $sdkCacheFileTemp 'sdk.txt'
+      } catch {
+        # Somebody beat us
+        Remove-Item -Path $sdkCacheFileTemp
+      }
+    }
   }
 
   # Add dotnet to PATH. This prevents any bare invocation of dotnet in custom
@@ -216,7 +232,10 @@ function InstallDotNet([string] $dotnetRoot,
       }
       catch {
         Write-PipelineTelemetryError -Category 'InitializeToolset' -Message "Failed to install dotnet runtime '$runtime' from custom location '$runtimeSourceFeed'."
+        ExitWithExitCode 1
       }
+    } else {
+      ExitWithExitCode 1
     }
   }
 }
@@ -274,8 +293,11 @@ function InitializeVisualStudioMSBuild([bool]$install, [object]$vsRequirements =
       $vsMajorVersion = $vsMinVersion.Major
       $xcopyMSBuildVersion = "$vsMajorVersion.$($vsMinVersion.Minor).0-alpha"
     }
-
-    $vsInstallDir = InitializeXCopyMSBuild $xcopyMSBuildVersion $install
+    
+    $vsInstallDir = $null
+    if ($xcopyMSBuildVersion.Trim() -ine "none") {
+        $vsInstallDir = InitializeXCopyMSBuild $xcopyMSBuildVersion $install
+    }
     if ($vsInstallDir -eq $null) {
       throw 'Unable to find Visual Studio that has required version and components installed'
     }