MDEV-15471 Isolate/sandbox PAM modules, so that they can't crash the server

tests fixed.

mysql-test/suite/plugins/r/pam_v1.result

+install plugin pam soname 'auth_pam_v1.so';
+create user test_pam identified via pam using 'mariadb_mtr';
+create user pam_test;
+grant proxy on pam_test to test_pam;
+#
+# athentication is successful, challenge/pin are ok
+# note that current_user() differs from user()
+#
+Challenge input first.
+Enter: not very secret challenge
+Now, the magic number!
+PIN: ****
+select user(), current_user(), database();
+user()	current_user()	database()
+test_pam@localhost	pam_test@%	test
+#
+# athentication is unsuccessful
+#
+Challenge input first.
+Enter: not very secret challenge
+Now, the magic number!
+PIN: ****
+drop user test_pam;
+drop user pam_test;
+uninstall plugin pam;

mysql-test/suite/plugins/t/pam.test

-
+let $PAM_PLUGIN_VERSION= $AUTH_PAM_SO;
 --source pam_init.inc
 
 --write_file $MYSQLTEST_VARDIR/tmp/pam_good.txt

mysql-test/suite/plugins/t/pam_init.inc

 
 --source include/not_embedded.inc
 
-if (!$AUTH_PAM_SO) {
+if (!$PAM_PLUGIN_VERSION) {
   skip No pam auth plugin;
 }
 
-eval install plugin pam soname '$AUTH_PAM_SO';
+eval install plugin pam soname '$PAM_PLUGIN_VERSION';
 create user test_pam identified via pam using 'mariadb_mtr';
 create user pam_test;
 grant proxy on pam_test to test_pam;

mysql-test/suite/plugins/t/pam_init_v1.inc

-
---source include/not_embedded.inc
-
-if (!$AUTH_PAM_V1_SO) {
-  skip No pam auth plugin;
-}
-
-eval install plugin pam soname '$AUTH_PAM_V1_SO';
-create user test_pam identified via pam using 'mariadb_mtr';
-create user pam_test;
-grant proxy on pam_test to test_pam;
-
-let $plugindir=`SELECT @@global.plugin_dir`;
-

mysql-test/suite/plugins/t/pam_v1.test

-
+let $PAM_PLUGIN_VERSION= $AUTH_PAM_V1_SO;
 --source pam_init.inc
 
 --write_file $MYSQLTEST_VARDIR/tmp/pam_good.txt
@@ -25,12 +25,6 @@ EOF
 --error 1
 --exec $MYSQL_TEST -u test_pam --plugin-dir=$plugindir < $MYSQLTEST_VARDIR/tmp/pam_bad.txt
 
---echo #
---echo # pam module crashes
---echo #
---error 1
---exec $MYSQL_TEST -u crash_pam_tool --plugin-dir=$plugindir < $MYSQLTEST_VARDIR/tmp/pam_good.txt
-
 --remove_file $MYSQLTEST_VARDIR/tmp/pam_good.txt
 --remove_file $MYSQLTEST_VARDIR/tmp/pam_bad.txt
 drop user test_pam;