duemir spotted this series of errors when using Evergreen on a poor network connection.

It appears that there are a number of invalid respoonses, perhaps from a captive portal or otherwise, which are being saved as .hpi files and then obviously fail to load.

The client has the checksums to do integrity checking already, so we should be performing that validation and retrying.

If clients are consistently failing to download artifacts, then we're going to have to figure out some reasonable way to inform the user, which is a bit out of the scope for this bug IMO