Add autoload for test modules (#3342)

Related #3238

1. Add autoload for test modules
2. Move TestHostCS.psm1 to 'test\tools\Modules\' folder
3. Remove explicit load TestHostCS.psm1 from test files

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

@@ -1,6 +1,3 @@
-$hostmodule = Join-Path $PSScriptRoot "../../Common/TestHostCS.psm1"
-import-module $hostmodule -ErrorAction SilentlyContinue
-
 Describe "Read-Host Test" -tag "CI" {
     BeforeAll {
         $th = New-TestHost

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

@@ -48,8 +48,6 @@ Describe "Write-Host with wrong colors" -Tags "CI" {
 Describe "Write-Host with TestHostCS" -Tags "CI" {
 
     BeforeAll {
-        $hostmodule = Join-Path $PSScriptRoot "../../Common/TestHostCS.psm1"
-        import-module $hostmodule -ErrorAction SilentlyContinue
         $th = New-TestHost
         $rs = [runspacefactory]::Createrunspace($th)
         $rs.open()