[AUDIT] LOGIN message credentials

Attached is a new patch that solves the issue of getting valid credentials 
into the LOGIN message. The current code was assuming that the audit context 
had already been copied. This is not always the case for LOGIN messages.

To solve the problem, the patch passes the task struct to the function that 
emits the message where it can get valid credentials.

Signed-off-by: Steve Grubb <sgrubb@redhat.com>
Signed-off-by: David Woodhouse <dwmw2@infradead.org>