Fix typo when getting Core build output location

Fail build if we fail to build PowerShell.exe before running tests
Fail build if we fail to push an artifact because it doesn't exist.

appveyor.yml

@@ -38,9 +38,13 @@ test_script:
       $ErrorActionPreference = 'Stop'
       #
       # CoreCLR
-      $env:CoreOutput = Split-Path -Parent (Get-PSOutput -Options (New-PSOptions -Publish -Configuration $buildConfiguratio))
+      $env:CoreOutput = Split-Path -Parent (Get-PSOutput -Options (New-PSOptions -Publish -Configuration $buildConfiguration))
       Write-Host -Foreground Green 'Run CoreCLR tests'
       $testResultsFile = "$pwd\TestsResults.xml"
+      if(!(Test-Path "$env:CoreOutput\powershell.exe"))
+      {
+         throw "CoreCL PowerShell.exe was not built"
+      }
       & ("$env:CoreOutput\powershell.exe") -noprofile -noninteractive -c "Set-ExecutionPolicy -Scope Process Unrestricted; Invoke-Pester test/powershell -Tag 'CI' -ExcludeTag 'Slow' -OutputFormat NUnitXml -OutputFile $testResultsFile"
                                                                                                        
       (New-Object 'System.Net.WebClient').UploadFile("https://ci.appveyor.com/api/testresults/nunit/$($env:APPVEYOR_JOB_ID)", (Resolve-Path $testResultsFile))
@@ -111,10 +115,23 @@ on_finish:
 
         $artifacts += (ls .\nuget-artifacts | % {$_.FullName})
 
+        $pushedAllArtifacts = $true
         $artifacts | % { 
             Write-Host "Pushing $_ as Appveyor artifact"
-            Push-AppveyorArtifact $_
+            if(Test-Path $_)
+            {
+              Push-AppveyorArtifact $_
+            }
+            else
+            {
+              $pushedAllArtifacts = $false
+              Write-Warning "Artifact $_ does not exist."
+            }
           }
+        if(!$pushedAllArtifacts)
+        {
+          throw "Some artifacts did not exist!"
+        }
       } catch {
         Write-Host -Foreground Red $_
       }