msi_full_path not translated to value in windows.pp

[shbakesas]

Line 51 of windows.pp has:

    $fileStream = [system.io.file]::openread('${msi_full_path}');

This is causing the assertion to fail because '${msi_full_path}' is being sent as the actual string instead of the value of the variable. Since $msi_full_path is not defined on the local OS, the assertion fails:

Debug: /Stage[main]/Datadog_agent::Windows/Exec[assert-acceptable-msi]/unless: Exception calling "OpenRead" with "1" argument(s): "Could not find file 'C:\Windows\system32\${msi_full_path}'."

This line should be updated to use double-quotes instead of single-quotes.
$fileStream = [system.io.file]::openread("${msi_full_path}");