tests: fix sss_nss_idmap-tests
If sss_nss_idmap-tests is complied with -Wl,-Bsymbolic-functions it
fails because sss_nss_make_request_timeout() is not properly wrapped but
the tests expects that the replacement call it provides is picked by the
linker and not the original function.
This patch wraps the call in the corresponding test library. As a
consequence a small helper function had to be added to make dlopen-tests
pass for the test library as well.
Reviewed-by: Fabiano Fidêncio <email@example.com>
Tested-by: Andreas Hasenack <firstname.lastname@example.org>