(chocolateyGH-520) Fix: Debug/Verbose messages not logged

`Write-Debug` / `Write-Verbose` messages are not being logged when
coming from the `chocolateyInstall`/`chocolateyUninstall` scripts. This
is due to `DebugPreference` / `VerbosePreference` being only set to
script level in the module and not global.

Instead of changing a global variable, also set the Debug and Verbose
preferences in the script runner. It is thought that changing a global
variable could have other unintended consequences if someone was
running these scripts directly from PowerShell. So prefer the script
level change.

src/chocolatey.resources/helpers/chocolateyScriptRunner.ps1

@@ -7,6 +7,11 @@
   [string]$packageScript
 )
 
+$DebugPreference = "SilentlyContinue"
+if ($env:ChocolateyEnvironmentDebug -eq 'true') { $DebugPreference = "Continue"; }
+$VerbosePreference = "SilentlyContinue"
+if ($env:ChocolateyEnvironmentVerbose -eq 'true') { $VerbosePreference = "Continue"; $verbosity = $true }
+
 Write-Debug "Running 'ChocolateyScriptRunner' for $($env:packageName) v$($env:packageVersion) with packageScript `'$packageScript`', packageFolder:`'$($env:packageFolder)`', installArguments: `'$installArguments`', packageParameters: `'$packageParameters`',"
 
 ## Set the culture to invariant