(GH-274) nuget: Clean up how debugMode is expressed

Previously we had an if condition on debugMode, but it is more
concise to just express it as a string appended to the list
of options passed to choco.

nuget/chocolatey/tools/chocolateysetup.psm1

@@ -4,7 +4,7 @@ $sysDrive = $env:SystemDrive
 $tempDir = $env:TEMP
 $defaultChocolateyPathOld = "$sysDrive\Chocolatey"
 #$ErrorActionPreference = 'Stop'
-$debugMode = $false
+$debugModeParams = ""
 
 function Initialize-Chocolatey {
 <#
@@ -34,17 +34,13 @@ param(
   Write-Debug "Initialize-Chocolatey"
 
   if ($env:ChocolateyEnvironmentDebug -eq 'true') {
-    $debugMode = $true
+    $debugMode = "dv"
   }
 
   Install-DotNet4IfMissing
 
   $chocoNew = Join-Path $thisScriptFolder 'chocolateyInstall\choco.exe'
-  if ($debugMode) {
-    & $chocoNew unpackself -fdvy
-  } else {
-    & $chocoNew unpackself -fy
-  }
+  & $chocoNew unpackself -fy$debugModeParams
 
   $installModule = Join-Path $thisScriptFolder 'chocolateyInstall\helpers\chocolateyInstaller.psm1'
   Import-Module $installModule -Force