audit: fix dangling keywords in audit_log_set_loginuid() output

Remove spaces between "new", "old" label modifiers and "auid", "ses" labels in
log output since userspace tools can't parse orphaned keywords.

Make variable names more consistent and intuitive.

Make audit_log_format() argument code easier to read.

Signed-off-by: Richard Guy Briggs <rgb@redhat.com>
Signed-off-by: Eric Paris <eparis@redhat.com>