Lookup username from uuid

Lookup username from uuid

When using the uid feature of the firewall module,
it did not work with string based usernames as
documented.

The uid propery always synchronized with a message of
<number> does not match <username>.

This code overrides the uid getter method to perform
a check of both the data from the property hash as well
as using that data (assuming it is a uid) to resolve the
username.

While this patch is pretty simple, I have only tested it
on Ubuntu 14.04. I am not sure if it could be problematic
with other versions.

I have not yet written tests b/c I wanted to submit
my proposed fix for discussion while I get those
written.