add test, simpler kwargs for flash function signature

tests/utils/test_flash.py

@@ -0,0 +1,10 @@
+from atst.utils.flash import formatted_flash as flash
+from flask import get_flashed_messages
+
+
+def test_flash_message():
+    flash("revoked_workspace_access", member_name="Lando")
+    messages = get_flashed_messages()
+    message_info = messages[0]
+    assert "message" in message_info
+    assert "Lando" in message_info["message"]