Fixed return type annotation in iptables module

Changed evaluate_command_policy return type from Result to str,
since Result.KEPT and Result.REPAIRED are string class attributes,
not Result instances.

Signed-off-by: Lars Erik Wik <lars.erik.wik@northern.tech>

Author: larsewi

promise-types/iptables/iptables.py

@@ -231,7 +231,7 @@ def evaluate_promise(self, promiser: str, attributes: Dict, metadata: Dict):
 
         return result, classes
 
-    def evaluate_command_policy(self, executable, table, chain, target) -> Result:
+    def evaluate_command_policy(self, executable, table, chain, target) -> str:
         policy_rules = self._iptables_policy_rules_of(executable, table, chain)
         assert len(policy_rules) == 1 and len(policy_rules[0].split()) >= 1