(QA-753) Make sure to still support saving MSIs locally

The initial commit for QA-753 didn't account for the MSI case, which
still requires saving the .msi file locally. This adds a save_locally
option to the cURL command line, based on whether we're fetch an msi.
Merge pull request #122 from branan/fix_windows_pe_installation

(QA-753) Make sure to still support saving MSIs locally