tap-solaris: Convert tap_open() to Error

Fixes inappropriate use of syslog().

Not fixed: leaks on error paths, suspicious non-fatal errors.  FIXMEs
added instead.

Signed-off-by: Markus Armbruster <armbru@redhat.com>
Reviewed-by: Eric Blake <eblake@redhat.com>
Message-id: 1431691143-1015-14-git-send-email-armbru@redhat.com
Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>
