Added testcase for acl_roles.

The testcase checks to see if the create user command sets the is_role column
to 'N' by default

mysql-test/r/acl_roles_default_create_user_not_role.result

+use mysql;
+create user 'test'@'localhost';
+select user, host, is_role from user where user='test' and host='localhost';
+user	host	is_role
+test	localhost	N
+drop user 'test'@'localhost';

mysql-test/t/acl_roles_default_create_user_not_role.test

+connect (mysql, localhost, root,,);
+use mysql;
+create user 'test'@'localhost';
+
+#check to see if a created user is not a role by default
+select user, host, is_role from user where user='test' and host='localhost';
+
+drop user 'test'@'localhost';
+disconnect mysql;