CVEscan should catch network issues and not crash

[kfiresmith]

In environments that need proxy which a user might not have set one, the cvescan application eventually times out and emits a long (75 line) traceback.

This is ugly and should be caught, instead only providing the useful error message that is printed right before the traceback:

❌ Download Failed!

...which prints off most consoles quickly due to the long traceback.

[gaby]

Ran into the same problem, should be an easy fix.