Extend NSS test suite

* nss/nss_test.h: New.
* nss/nss_test1.h: Rewrite to use test-provided data.  Add group
tests.  Parameterize to allow multiple instances.
* nss/nss_test2.h: New.  Second instance.
* nss/nss_test.ver: New.
* nss/nss_test1.c: Update to use new framework.
* nss/nss_test2.c: New.
* nss/nss_test3.c: New.
* nss/nss_test4.c: New.
* nss/nss_test5.c: New.
* nss/Makefile: Build new tests.
* shlib-versions: Add libnss_test2.