Add ability to use string path for sock instead of forcing user to manually create socket.

sanic/server.py

@@ -568,11 +568,14 @@ def serve(host, port, request_handler, error_handler, before_start=None,
     )
 
     if isinstance(sock, str):
-        _create_server = loop.create_unix_server
+        server_coroutine = loop.create_unix_server(
+            server,
+            path=sock,
+            ssl=ssl,
+            backlog=backlog
+        )
     else:
-        _create_server = loop.create_server
-
-    server_coroutine = _create_server(
+        server_coroutine = loop.create_server(
             server,
             host,
             port,