selftest: updated docs.py script

selftest: updated docs.py script

The script now checks the parameter defaults against the documentation by using
the output of testparm and samba-tool testparm.

It now also uses the ElementTree xml library.

Change-Id: I2657c8c56a8c8383735e659dc9f636b4c5ab460b
Signed-off-by: Garming Sam <garming@catalyst.net.nz>
Signed-off-by: Andrew Bartlett <abartlet@samba.org>
Reviewed-by: Michael Adam <obnox@samba.org>
Autobuild-User(master): Michael Adam <obnox@samba.org>
Autobuild-Date(master): Fri Jan 31 23:22:09 CET 2014 on sn-devel-104