gp_inf: Read/write files with a UTF-16LE BOM in GptTmpl.inf

gp_inf: Read/write files with a UTF-16LE BOM in GptTmpl.inf

Regression caused by 16596842a62bec0a9d974c48d64000e3c079254e

[MS-GPSB] 2.2 Message Syntax says that you have to write a BOM which I
didn't do up until this patch. UTF-16 as input encoding was marked much
higher up in the inheritance tree, which got overriden with the Python 3
fixes. I've now marked the encoding much more obviously for this file.

BUG: https://bugzilla.samba.org/show_bug.cgi?id=14004

Signed-off-by: Garming Sam <garming@catalyst.net.nz>
Reviewed-by: Gary Lockyer <gary@catalyst.net.nz>
Autobuild-User(master): Gary Lockyer <gary@samba.org>
Autobuild-Date(master): Fri Jul 19 02:20:47 UTC 2019 on sn-devel-184