lib/param: handle (ignore) substitution variable in smb.conf

lib/param: handle (ignore) substitution variable in smb.conf

BUG: https://bugzilla.samba.org/show_bug.cgi?id=10722

The function handle_include returns false when trying to include
files that have a substitution variable in filename (like %U),
this patch makes handle_include to ignore this case, to make
samba-tool work when there is such include in samba's configuration.

Error was :
	root@ubuntu:/usr/local/samba# grep 'include.*%U' etc/smb.conf
	include = %U.conf
	root@ubuntu:/usr/local/samba# ./bin/samba-tool user list
	Can't find include file %U.conf
	ERROR(runtime): uncaught exception - Unable to load default file

Signed-off-by: Quentin Gibeaux <qgibeaux@iris-tech.fr>
Reviewed-by: Michael Adam <obnox@samba.org>
Reviewed-by: Jeremy Allison <jra@samba.org>
Autobuild-User(master): Jeremy Allison <jra@samba.org>
Autobuild-Date(master): Wed Dec  9 02:05:30 CET 2015 on sn-devel-104