[Ignore] Allow VSTS env var override (#2264)

Author: rjmholt

tools/releaseBuild/setVstsVariables.ps1

@@ -5,6 +5,12 @@ $vstsVariables = @{
 # Use VSTS's API to set an env vars
 foreach ($var in $vstsVariables.Keys)
 {
+    # Allow environment to override
+    if (Get-Item "env:$var" -ErrorAction Ignore)
+    {
+        continue
+    }
+
     $val = $vstsVariables[$var]
     Write-Host "Setting var '$var' to value '$val'"
     Write-Host "##vso[task.setvariable variable=$var]$val"