Remove hardcoded download path

Previously all files got downloaded to a hardcoded path, including the
username for the CI machines. Usually, it does not fit the username of a
local development machine, complicating to reproduce bugs.

Introduce Get-(Default)DownloadLocation functions in helpers to
specify the default download location. This helps to run the
provisioning scripts on a local machine.

Change-Id: I761a92bf5e3e774358756a95dddb9a5d6ee54db9
Reviewed-by: Oliver Wolff <oliver.wolff@qt.io>

coin/provisioning/common/windows/libclang.ps1

@@ -16,7 +16,7 @@ Get-Content "$PSScriptRoot\..\shared\sw_versions.txt" | Foreach-Object {
     $libclang_version = $libclang_version -replace '["."]'
 }
 
-$zip = "c:\users\qt\downloads\libclang.7z"
+$zip = Get-DownloadLocation "libclang.7z"
 $baseDestination = "C:\Utils\libclang-" + $libclang_version + "-" + $toolchain
 
 function setURL() {