Panel_Iframe - Allow relative urls in config (#11832)

* Panel_Iframe - Allow relative urls in config

* change regex to check for starting forward slash only

* Change error message and const name

tests/components/test_panel_iframe.py

@@ -11,11 +11,11 @@ from tests.common import get_test_home_assistant
 class TestPanelIframe(unittest.TestCase):
     """Test the panel_iframe component."""
 
-    def setup_method(self, method):
+    def setUp(self):
         """Setup things to be run when tests are started."""
         self.hass = get_test_home_assistant()
 
-    def teardown_method(self, method):
+    def tearDown(self):
         """Stop everything that was started."""
         self.hass.stop()
 
@@ -50,6 +50,11 @@ class TestPanelIframe(unittest.TestCase):
                         'title': 'Weather',
                         'url': 'https://www.wunderground.com/us/ca/san-diego',
                     },
+                    'api': {
+                        'icon': 'mdi:weather',
+                        'title': 'Api',
+                        'url': '/api',
+                    },
                 },
             })
 
@@ -72,3 +77,12 @@ class TestPanelIframe(unittest.TestCase):
             'url': '/frontend_es5/panels/ha-panel-iframe-md5md5.html',
             'url_path': 'weather',
         }
+
+        assert panels.get('api').to_response(self.hass, None) == {
+            'component_name': 'iframe',
+            'config': {'url': '/api'},
+            'icon': 'mdi:weather',
+            'title': 'Api',
+            'url': '/frontend_es5/panels/ha-panel-iframe-md5md5.html',
+            'url_path': 'api',
+        }