Use split_port for ports format check

Rather than implement the logic a second time, use docker-py
split_port function to test if the ports is valid.

Signed-off-by: Mazz Mosley <mazz@houseofmnowster.com>

compose/config/validation.py

@@ -1,5 +1,6 @@
 import os
 
+from docker.utils.ports import split_port
 import json
 from jsonschema import Draft4Validator, FormatChecker, ValidationError
 
@@ -26,26 +27,13 @@ DOCKER_CONFIG_HINTS = {
 VALID_NAME_CHARS = '[a-zA-Z0-9\._\-]'
 
 
-@FormatChecker.cls_checks(format="ports", raises=ValidationError("Ports is incorrectly formatted."))
+@FormatChecker.cls_checks(format="ports", raises=ValidationError("Invalid port formatting, it should be '[[remote_ip:]remote_port:]port[/protocol]'"))
 def format_ports(instance):
-    def _is_valid(port):
-        if ':' in port or '/' in port:
-            return True
-        try:
-            int(port)
-            return True
-        except ValueError:
-            return False
+    try:
+        split_port(instance)
+    except ValueError:
         return False
-
-    if isinstance(instance, list):
-        for port in instance:
-            if not _is_valid(port):
-                return False
-        return True
-    elif isinstance(instance, str):
-        return _is_valid(instance)
-    return False
+    return True
 
 
 def get_unsupported_config_msg(service_name, error_key):