selftest: Fix timestamps on FreeBSD 11

selftest: Fix timestamps on FreeBSD 11

FreeBSD's date does not print the %, and \? does not catch that

Tested this manually:

$ echo 'time: 2016-11-23 12:52:19.123456Z'| sed 's/\..*NZ$/.000000Z/'
time: 2016-11-23 12:52:19.123456Z
$ echo 'time: 2016-11-23 12:52:19.%6NZ'| sed 's/\..*NZ$/.000000Z/'
time: 2016-11-23 12:52:19.000000Z
$ echo 'time: 2016-11-23 12:52:19.6NZ'| sed 's/\..*NZ$/.000000Z/'
time: 2016-11-23 12:52:19.000000Z
$ echo 'time: 2016-11-23 12:52:19.NZ'| sed 's/\..*NZ$/.000000Z/'
time: 2016-11-23 12:52:19.000000Z
$

Signed-off-by: Volker Lendecke <vl@samba.org>
Reviewed-by: Michael Adam <obnox@samba.org>
Autobuild-User(master): Michael Adam <obnox@samba.org>
Autobuild-Date(master): Thu Nov 24 00:42:55 CET 2016 on sn-devel-144