install-jar: avoid silent swallowing of curl download failure

[soxofaan]

When you use geopyspark install-jar to download the backend jar, and something goes wrong with the curl command, the user doesn't really notice this.

For example: I was working with a forked version of geopyspark, which had a custom version defined in geopyspark_constants.py. I ran geopyspark install-jar to download the jar and that seemed to work. After losing quite some time troubleshooting, I found out that `geotrellis-backend-assembly-foobar.jar' was a very small file, just containing the text "Not Found" :/

This PR addresses this by making sure an exception is raised when the download encounters 4xx or 5xx http codes so the user will know earlier that something is wrong. It also add showing the download URL and target path for easier troubleshooting