ec2: check for changes

In the ec2 module, if an id is specified, check if there have been
any changes. If not, return changed=False

Fixes #3746

cloud/ec2

@@ -396,7 +396,10 @@ def create_instances(module, ec2):
 
     # Both min_count and max_count equal count parameter. This means the launch request is explicit (we want count, or fail) in how many instances we want.
 
-    if count_remaining > 0:
+    if count_remaining == 0:
+        changed = False
+    else:
+        changed = True
         try:
             params = {'image_id': image,
                       'key_name': key_name,
@@ -465,7 +468,7 @@ def create_instances(module, ec2):
         created_instance_ids.append(inst.id)
         instance_dict_array.append(d)
 
-    return (instance_dict_array, created_instance_ids)
+    return (instance_dict_array, created_instance_ids, changed)
 
 
 def terminate_instances(module, ec2, instance_ids):
@@ -578,14 +581,13 @@ def main():
 
     elif module.params.get('state') == 'present':
         # Changed is always set to true when provisioning new instances
-        changed = True
         if not module.params.get('key_name'):
             module.fail_json(msg='key_name parameter is required for new instance')
         if not module.params.get('image'):
             module.fail_json(msg='image parameter is required for new instance')
-        (instance_dict_array, new_instance_ids) = create_instances(module, ec2)
+        (instance_dict_array, new_instance_ids, changed) = create_instances(module, ec2)
 
-    module.exit_json(changed=True, instance_ids=new_instance_ids, instances=instance_dict_array)
+    module.exit_json(changed=changed, instance_ids=new_instance_ids, instances=instance_dict_array)
 
 
 # this is magic, see lib/ansible/module_common.py