Make the error and warning message tests a first class test script; in
gitlab CI, failures would not necessarily result in output being
captured.
Signed-off-by: Steve Beattie <steve.beattie@canonical.com>
Acked-by: John Johansen <john.johansen@canonical.com>
MR: https://gitlab.com/apparmor/apparmor/-/merge_requests/522
