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.

src/test/modules/test_rls_hooks/expected/test_rls_hooks.out

+LOAD 'test_rls_hooks';
 CREATE TABLE rls_test_permissive (
     username        name,
     supervisor      name,
@@ -191,3 +192,9 @@ ERROR:  new row violates WITH CHECK OPTION for "rls_test_both"
 -- failure
 INSERT INTO rls_test_both VALUES ('r4','s4',7);
 ERROR:  new row violates WITH CHECK OPTION for "rls_test_both"
+RESET ROLE;
+DROP TABLE rls_test_restrictive;
+DROP TABLE rls_test_permissive;
+DROP TABLE rls_test_both;
+DROP ROLE r1;
+DROP ROLE s1;

src/test/modules/test_rls_hooks/sql/test_rls_hooks.sql

+LOAD 'test_rls_hooks';
+
 CREATE TABLE rls_test_permissive (
     username        name,
     supervisor      name,
@@ -155,3 +157,12 @@ INSERT INTO rls_test_both VALUES ('r1','s1',7);
 
 -- failure
 INSERT INTO rls_test_both VALUES ('r4','s4',7);
+
+RESET ROLE;
+
+DROP TABLE rls_test_restrictive;
+DROP TABLE rls_test_permissive;
+DROP TABLE rls_test_both;
+
+DROP ROLE r1;
+DROP ROLE s1;