Fix Write-Host tests

These were not testing the development build of PowerShell.

test/powershell/Modules/Microsoft.PowerShell.Utility/Write-Host.Tests.ps1

@@ -1,22 +1,18 @@
-Describe "Write-Host DRT Unit Tests" -Tags DRT{ 
+Describe "Write-Host DRT Unit Tests" -Tags DRT {
+
+    BeforeAll {
+        $powershell = Join-Path -Path $PsHome -ChildPath "powershell"
+    }
+
+
     $testData = @(
         @{ Name = 'NoNewline';Command = "Write-Host a,b -Separator ',' -ForegroundColor Yellow -BackgroundColor DarkBlue -NoNewline"; returnValue = "a,b" }
         @{ Name = 'Separator';Command = "Write-Host a,b,c -Separator '+'"; returnValue = "a+b+c" }
     )
-   
-    It "write-Host works with '<Name>' switch" -TestCases $testData -Pending:$IsOSX { 
-        param($Command, $returnValue) 
 
-        If($IsLinux)
-        {
-            $content = powershell  -noprofile -command $Command
-        }
-        
-        If ($IsWindows)
-        {
-            $content = powershell.exe -noprofile -command $Command
-        }
+    It "write-Host works with '<Name>' switch" -TestCases $testData -Pending:$IsOSX {
+        param($Command, $returnValue)
 
-        $content | Should Be $returnValue
+        & $powershell -noprofile $Command | Should Be $returnValue
     }
-}
+}