Networking error ENONET when no internet connectivity

Serverless dynamodb local plugin is not working as expected when there is no internet connectivity.

When i tried to start the dynamodb local using following command, getting ENONET error.
```
sls dynamodb start --migrate
```
Error captured using **SLS_DEBUG=***

**Expected Behavior :** Plugin should work, when there is no internet connectivity for offline development

**_Note: It is working perfectly when internet connectivity is available._**

Start by reproducing `sls dynamodb start --migrate` with internet connectivity disabled and inspect the SLS_DEBUG output shown in the issue. Trace the startup path that attempts network access; done means the local DynamoDB plugin starts and migrates successfully without an internet connection.

Written by the indexing model from the issue text.