fix(aws): complete instance_profile->machine_role rename

Finish the instance_profile->machine_role rename in base context flags
that was missed in the earlier AWS handler migration.

Author: fgogolli

tests/providers/aws/unit/test_base_context_mixin.py

@@ -214,6 +214,7 @@ def test_prepare_standard_flags_minimal(self):
         self.template.subnet_ids = None
         self.template.security_group_ids = None
         self.template.instance_types = None
+        self.template.machine_role = None
 
         result = self.mixin._prepare_standard_flags(self.template)