wafsamba: detect programmer errors in CHECK_BUNDLED_SYSTEM()

wafsamba: detect programmer errors in CHECK_BUNDLED_SYSTEM()

All prerequisite libraries of CHECK_BUNDLED_SYSTEM[_PKG](onlyif='lib1 lib2')
need to be checked before.

That means conf.env['FOUND_SYSTEMLIB_lib1'] and conf.env['FOUND_SYSTEMLIB_lib2']
need to exist independed of its value (True or False). Otherwise this is a logic error.

BUG: https://bugzilla.samba.org/show_bug.cgi?id=11458

Signed-off-by: Stefan Metzmacher <metze@samba.org>
Reviewed-by: Ralph Boehme <slow@samba.org>
Autobuild-User(master): Stefan Metzmacher <metze@samba.org>
Autobuild-Date(master): Wed Nov  4 18:38:18 CET 2015 on sn-devel-104