setpriv: Fix --apparmor-profile

There were two bugs.  First, trying to access /proc/self/attr/exec
with O_CREAT | O_EXCL has no chance of working.  Second, it turns
out that the correct command to send is "exec", not "changeprofile".
Of course, there was no way to know this until:

    commit 3eea57c26e49a5add4c053a031cc2a1977b7c48e
    Author: John Johansen <john.johansen@canonical.com>
    Date:   Wed Feb 27 03:44:40 2013 -0800

        apparmor: fix setprocattr arg processing for onexec

Signed-off-by: Andy Lutomirski <luto@amacapital.net>
getopt.1: The usual doc dir is /usr/share/doc, not .../docs

Signed-off-by: Ville Skyttä <ville.skytta@iki.fi>