vulnfeeds: support re-evaluating existing entries

[westonsteimel]

I don't believe it is currently possible to re-evaluate an existing entry. It would be useful to re-run analysis over existing entries when we add enhancements to the code to better classify things, etc. It would also be useful for cases where there is no fixed version at the time an advisory is published, but a fixed version is later released. Currently I just have some python scripts I run manually to try and check some of this and manually update when needed.

[oliverchang]

Indeed! This is an important feature we need to support.