(GH-274) Allow unattended installs as non-admin user

Previously, if a non-admin user attempted to install chocolatey,
a message indicating that non-admin installs were for advanced
users only would appear and block the installation.

Advanced users know what they are doing, so allow them to
set the ChocolateyEnvironmentAllowGlobalConfirmation environment
variable, just like they can pass -y to any other invocation
of chocolatey.

nuget/chocolatey/tools/chocolateysetup.psm1

@@ -41,9 +41,9 @@ param(
 
   $chocoNew = Join-Path $thisScriptFolder 'chocolateyInstall\choco.exe'
   if ($debugMode) {
-    & $chocoNew unpackself -fdv
+    & $chocoNew unpackself -fdvy
   } else {
-    & $chocoNew unpackself -f
+    & $chocoNew unpackself -fy
   }
 
   $installModule = Join-Path $thisScriptFolder 'chocolateyInstall\helpers\chocolateyInstaller.psm1'
@@ -314,9 +314,9 @@ param(
   Copy-Item $chocoExe $chocoExeDest -force
 
   if ($debugMode) {
-    & $chocoExeDest unpackself -fdv
+    & $chocoExeDest unpackself -fdvy
   } else {
-    & $chocoExeDest unpackself -f
+    & $chocoExeDest unpackself -fy
   }
 }