[bug] Update MSIs aren't cleaned up from temp folder after update

[talzion12]

It seems that after an update is performed the MSI that was downloaded is not cleaned up. This can cause the disk to become full with MSIs in case the update is retried and fails to install repeatedly.

I believe there are a few options to improve the situation:

1. Be able to configure the download directory: this way the files can be periodically cleaned up.
2. Make the downloaded file have a deterministic name so that it just gets overwritten instead of filling up the disk with many identical temp files.

Both of these don't entirely fix the problem but they make it a bit more manageable in my opinion, let me know what you think.

[FabianLars]

tracking issue for nsis installer #2132