Tests: Add some PHP tests for 403 and 404 error handling.

Since the previous commit, we now properly handle 403 Forbidden & 404
Not Found errors in the PHP language module.

This adds a test for 403 Forbidden to test/test_php_application.py, but
also fixes a test in test/test_php_targets.py where we were checking for
503 but should have been a 404, which we now do.

Acked-by: Alejandro Colomar <alx@nginx.com>
Cc: Andrei Zeliankou <zelenkov@nginx.com>
[ Incorporates a couple of small test cleanups from Andrei ]
Signed-off-by: Andrew Clayton <a.clayton@nginx.com>

test/test_php_application.py

@@ -664,6 +664,26 @@ opcache.preload_user = %(user)s
             resp['headers']['Location'] == 'http://foo/path/'
         ), 'Location with custom Host over UDS'
 
+    def test_php_application_forbidden(self, temp_dir):
+        new_root = temp_dir + "/php-root"
+        os.makedirs(new_root + '/path')
+        os.chmod(new_root + '/path', 0o000)
+
+        assert 'success' in self.conf(
+            {
+                "listeners": {"*:7080": {"pass": "applications/php-path"}},
+                "applications": {
+                    "php-path": {
+                        "type": self.get_application_type(),
+                        "processes": {"spare": 0},
+                        "root": new_root,
+                    }
+                },
+            }
+        ), 'forbidden directory'
+
+        assert self.get(url='/path/')['status'] == 403, 'access forbidden'
+
     def test_php_application_extension_check(self, temp_dir):
         self.load('phpinfo')