Fix installcheck for test_rls_hooks

Fix installcheck for test_rls_hooks

As pointed out by the buildfarm, test_rls_hooks wasn't functioning
properly with a clean installcheck.  test_rls_hooks needs to explicitly
load the library with the hooks in it, to allow installcheck to work;
using the --temp-config doesn't help since that isn't used when running
installcheck and it isn't exactly fair to the buildfarm to modify the
installed config prior to calling installcheck.

Also, have test_rls_hooks clean up after itself.